The Dayoukeng Crater in Yangmingshan National Park is the biggest sulfur vent area in Taiwan, and would likely be the first place to spew lava in the event of a volcanic eruption. This along with Turtle Island are the two known active volcanos in Taiwan. The area was also an important historical sulfur mine. Currently access to Dayoukeng is closed, but you can fly a drone hear with a permit.

Background:
The area known as Yangmingshan now was formed by volcanoes about 700,000 years ago, forming many mountains about 1000 meters or less in northwestern Taiwan. The park still features active volcanoes, vents, and hot springs.
The original name of the area was Caoshan (grass mountain 草山). During the Qing Dynasty, the area was used to harvest sulfur, and many of the hills were burned to help catch sulfur thieves. 
In 1927 during the Japanese era, Yangmingshan was made as the first national park in Taiwan, then known as Datunshan National Park Association. 
In 1950 after the ROC took Taiwan Chiang Kai-shek renamed the park after the philosopher Wang Yangming, and called the area Yangmingshan. 
In 1985, after resolving many land disputes, Yangmingshan National Park was officially designated as a national park in the ROC era. 
Dayoukeng (literally "Big Oil Crater" gets its name because the there are two main sulfur vents on Yangmingshan, and it is the biggest sulfur vent area in Taiwan. Temperatures here can reach 120 degrees celcious, and the water is very acidic with a PH level of only 1-2. The venting crater lies about 805 meters above sea level. A few kilometers under the ground, there is a leftover lava chamber from a previous eruption that heats up ground water and sends it spewing back to the surface.
Sulfur mining at Dayoukeng Crater in Yangmingshan National Park started in the Qing Dynasty by a British mining company who first obtained the rights to mine here in 1897. Currently you can find lots of old mining equipment that were abandoned here. The Yulu Old Trail was built near Dayoukeng to transport mining materials. Mining sulfur ended with the formation of Yangmingshan National Park. 
Dayoukeng lies in Jinshan District of New Taipei City. 
It is a popular stop in Yangmingshan and has two parking lots and visitor's center. It is also one of the starting points for the Mt. Qixing Trail. 

Hours:
The visitor's center is open from 9 AM to 4:30 PM.
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Price:
Free
(parking 30 NT)

How to get there:
By Car/Scooter: From Taipei, take provincial highway 2A north to the Zhizihu Lookout. Keep right until you reach the turnoff the the Qingtiangang parking lot. Car parking is limited on weekends and the number of cars allowed up the mountain is also limited. There is also paid scooter parking.
By Bus: From Beitou MRT Station, Take Little Bus 9 (小9) to Qingtiangang Station (擎天崗).
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Map:
Please see below: ​

Ever want to see an active volcano up close? You can at the mud Volcanos in Wushanding Nature Preserve, Yanchao District of Kaohsiung. These spew out mud all day, which piles up and then gets washed away by rain. It is a unique and beautiful geological oddity worth visiting. These are the largest and most concentrated mud volcanoes in Taiwan. 

Geological History:

Wushanding Mud Volcanoes are part of a stretch of badlands that cover a large swath of southern Taiwan near the central mountain range in rural Tainan and Kaohsiung. Typical badlands are found in dryer climates, are composed of sedimentary rocks, typically have very little vegetation, and have deep valleys or ravines. The badlands in Taiwan are unique in that they are in a tropical rain forest. How is this possible? 
The soil at Wushanding is composed of mudstone, sandstone, shale, and chalk. Because of high alkaline levels due to chalk in the soil, trees and grass cannot grow very well. The lack of vegetation as well as high rainfall gives way to quick eroding hills, or badlands. The local Rivers also helped to carve out the landscape and bare hills.
Due to vents in the earth's crust as well as deep pressures, water is pushed up to form these mud volcanoes. Nearby are also some natural gas vents, such as the ones at Guanziling Fire and Water Cave. The area around Yanchao is full of badlands and mud volcanoes, but the volcanoes at Wushanding are the most concentrated and pronounced in all of Taiwan. 
Wushanding was declared a protected area in 1992.
Because of limited public transportation, normally there are not too many visitors but the weekends can be busy.

Hours:
9 AM to 4:30 PM every day

Price:
Free! But you have to register in order to enter the park.

How to Get There:
By Bus: From Eda World, take bus 7A to Kaohsiung Normal University. It is about a 20 minute walk from the university. 
By Car/Scooter:
Take National Freeway 10 East out of Kaohsiung and get off at the Yanchao exit (or travel by scooter under the freeway). Then travel east on provincial highway 22 passed National Kaohsiung University of Science and Technology. You will have to use google Maps to turn left onto a one lane country back road to find the mud volcanoes. 
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Map:
Please refer to the map below:

Lovers Lake is a small lake a recreation area in Anle District of Keelung City. It has some easy trails, bridges, and a tower that looks over the area. The lake trails also connect to Dawulun Fort. Overall it is a nice scenic spot for a day trip in Northern Taiwan.

Background:
The name "Lovers Lake" comes from the fact that there are actually two lakes, one larger and one smaller, so they are a like a couple in love.
The sandstone that forms the area was created between 10 and 20 million years ago, and was pushed out of the sea along with northern Taiwan thousands of years ago. 
In the past the area was run by a private company, which went out of business. Recently the Keelung City government has taken over control, and has installed a trail that circles the lake.
There is also a suspension bridge, windmill, and stone tower overlooking the lake.
Nearby you can hike to Dawulun Fort or Eagle Rock that provide great views of the north coast.
Currently the lake is popular with hikers and intagrammers, as well as wedding photographers. On the weekends it can get quite busy and parking can be hard to find.

Hours:
24/7
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Price:
Free

How to get there:
By car/scooter: Take provincial highway northwest out of Keelung, and take a right on Jijin First Road toward Keelung Chang Kung Hospital. The Lover's lake parking lot is at the top of the hill before the road turns into one lane. There is limited parking, and you may have to park further away. The trail is not wheelchair or stroller friendly.
However there is always plenty of scooter parking.
By bus: Unfortunately there are no buses that directly get there, so you will have to walk from provincial highway 2, or take a taxi.

Map:
Please see below:

Bitou Cape (aka Bitoujiao/Bítóujiǎo) is a scenic area of coastline in Ruifang District of New Taipei, along the northeast coast, with popular hiking trails, interesting geological formations, a refurbished tourist military complex. and steep sea cliffs. It is a beautiful area along the coast that you should be sure to not miss. 

Background:
The sandstone that forms Bitou Cape was  formed as sediment under the ocean millions of years ago and were then uplifted thanks to the collision of the Eurasian and Philippine plates. The rocks are mainly sedimentary and are part of the same formation that forms the special rock formations on the northern coast around Keelung. Because of this, there are many interesting eroded rock formations around the cape.
The name Bitou (鼻頭) means the tip of the nose in Chinese.
Bitoujiao Lighthouse was completed in 1897, built by the Japanese. Later it was repaired in WWII, and is still used today.
The ROC army/navy military base at Bitou Cape has been sitting dormant for over 20 years, and was finally opened to the public as a rainbow "pink" military base to attract tourists on May 1st, 2020.
The area is a popular weekend destination for many residents of Northern Taiwan.

Hours:
24/7

Price:
Free

How to get there:
By Car/Scooter: From Keelung, take provincial highway 2 east along the north coast until you reach the Bitou Fishing Harbor. There is limited parking near the harbor, and further free parking on the other side of the tunnel but it is a bit of a walk. 
By Bus: From Keelung TRA Station, take Keelung Bus 791 east about two hours to Bitou cape. 

Map:
​Please see below:

Heping Island Park is a geo-park and water park on Heping Island, just outside of downtown Keelung. Here you can find many interesting rock formations in the sedimentary rock along the seashore. There are also salt water swimming pools, amazing places to go diving, a playground, hiking trails, and historical sights. Some would say this island is the world's best kept secret. It is definitely worth stopping here along Taiwan's northern coast.

Historical Background:
Heping Island was formed as sediment under the ocean millions of years ago and were then uplifted thanks to the collision of the Eurasian and Phillipine plates. The rocks have then been slowly eroded away by wind and water, creating odd shapes that you see today. You can see similar formations atYehliu Geopark. 
Heping island is the closest island to the main island of Taiwan. It first part of Basay aborigine lands. Chinese fisherman first called the island Greater Keelung Island.
The island was first settled by the Spanish in 1626, as their first settlement in what became their rule of northern Taiwan until they were defeated by the Dutch and left Taiwan in 1642. On Heping Island they built Fort San Salvador (聖薩爾瓦多城), which was destroyed and abandoned by the Dutch in 1668. The ruins of the fort were not confirmed to be found on the island until excavations in 2019.
After the Japanese occupation of Taiwan, the island was renamed Sheliao Island (社寮島). After WWII, as part of the White Terror Movement, on March 8th, 1947 KMT soldiers kidnapped and shot some of about 30 civilians on the island that were suspected enemy conspirators, known as the Sheliao Incident "社寮事件." After this, the people on the island decided to change to island's name to "Peace Island" or Heping Island in Chinese, so that the KMT would stop harassing the local people and bring peace to the island. 
The Island was under KMT military control until the 1970s, after which tourists were allowed to enter the island. 
Now it is a popular daytime and weekend destination for many Taiwanese.

Hours:
8 AM to 6 PM
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Price:
80 NT per person

When to go:
During the summer (May to November) when the water is warm and calm for swimming and diving.

How to get there:
By Car/Scooter: Take provincial highway 2 north out of Keelung and take a left at Zhengbin Road. Cross the bridge over to the island and head to the park which is on the north side of the island. There is paid parking in front of the park. 
By Bus: From Keelung, take Keeling Bus 101 to Heping Isand bus stop.

Map:
Please see below:

The 99 Peaks Trail (aka Jiujiufeng Forest Trail or 九十九峰) in Caotun Township of Nantou County is one of the most unique and beautiful places in Taiwan. It features extremely steep grassy hills that look like they are from a cartoon. This is due to the easily eroding sediment that they are made out of. Taiwan's torrential rains and earthquakes have sped up the erosion on these hills, making them especially steep and pointy, and creating what looks like 99 peaks on the horizon. From the trail one clearly see the jagged 99 peaks as well as beautiful views of Caotun and Nantou.

Background:
​The 99 Peaks are built on the same sediment as Huoyanshan, with iron rich soil that was deposited and lifted up due to tectonic forces.
Discoloration due to laterization (leaching and oxidation due to heavy rain) of minerals in the sediment has made the rocks near the top of the mountain here orange-red.
Like Tianliao Moon World (田寮月世界) and Liji Badlands （利吉惡地）, 99 Peaks is considered a badland due to fast erosion.
99 Peaks, Huoyanshan (火炎山), and Shibaluohan Mountain (十八羅漢山) make up the three "Huoyanshan formations" in Taiwan. 
The slopes here are very steep, and average from 60-80 degrees, making them impossible to cultivate. The entire mountain area is like a bunch of mini slot canyons.
At it's highest point, the 99 peaks are 779 meters above sea level, but were only 777 meters above sea level before the 921 earthquake. 
After the 921 earthquake, much of the soil on the mountain eroded away due to shaking, and the hills were left bare. Shortly after, the area was declared a nature reserve. 21 years after the earthquake, the hills are now covered in grass and shrubs. 
The trail doesn't go to the very top of the peaks, and if you venture further be careful because the cliffs are very steep on either side and erosion could happen at any time. 
As of March 2020, Nantou County has purchased the land of 99 Peaks for 100 million NT, in hopes of cultivating it for tourism, such as hot air balloon rides. Let's hope it becomes a major tourist destination!

Hours:
24/7

Price:
Free

Length:
1 KM one way
About 1 hour total
About 200 meters of elevation gain.

Difficulty:
Easy

How to get there:
By Car: Take National Freeway 6 toward Puli and get off at the east Caotun interchange. Then drive east on provincial highway 14 until you reach Jianxing Rad intersection on the other side of the river. Turn left and keep going until you reach the trail head. 
By Scooter: Ride east on provincial highway 14 until you reach Jianxing Rad intersection on the other side of the river. Turn left and keep going until you reach the trail head. 
By Bus: Take bus 6268A east out of Caotun and get off at Pinglin Station. From there it is about a 20 minute walk to the trailhead. 

Map:
Please see below:

Elephant Trunk Rock is a rock shaped like its name in the Shenao area of Ruifang District, New Taipei City. There are also many interesting rock formations in the area. It is one of the most recognizable rock formations on the north coast and a popular location for, kayakers, snorkelers, and instagrammers. 

Background:
The sandstone and sedimentary that forms the Elephant Rock formation was created between 10 and 20 million years ago, and was pushed out of the sea along with northern Taiwan thousands of years ago. 
The Elephant's head was formed by easily eroding sandstone, with the area under the trunk being eroded away by the sea and waves. 
Elephant Rock is so named because it looks like an elephant.
The area around Elephant Rock was a protected military base until the year 2000, after which civilians were allowed to freely visit.
Kayaking and Snorkeling are also popular activities near the Elephant Rock.

Hours:
24/7

Price:
Free

How to get there:
By Car/Scooter: Drive to Keelung, then from downtown take provincial highway 2 east about 10 KM until you reach the Shenziao harbor, and there is some paid parking if you drive to the very end, which will put you closest to Elephant Trunk Rock.
​By Train/Bus: Take the TRA to Badouzi (八斗子） station, then walk about 1 KM east until you reach the elephant rock on the coast. 

Map:
Please see below:

Yehliu is perhaps the most famous geological park in Taiwan, with its most famous landmark being the Queen's Head rock. These rock formations have been forming for thousands of years through erosion of soft sandstone due to wind and water. Hurry and see these formations soon before they are gone forever!

Background:
The sandstone that forms the Yehliu formation was created between 10 and 20 million years ago, and was pushed out of the sea along with northern Taiwan thousands of years ago. 
The Queen's head is formed by two layers of sandstone, one soft fast eroding layer on bottom and a harder layer on top. This kind of sandstone formation can be seen around the world and is known as a hoodoo. The Queen's head was named after Queen Elizabeth I, because it is thought to look like her. 
The head is eroding .2 to .5 CM per year and is expected to fall at any time!
The name Yehliu comes from the Spanish name for the area "Putno Diablos" which was then also used by the Dutch, and transliterated by the Chinese settlers in the area as "Yehliu" in Chinese. 

Yehliu Ocean world is the largest aquarium in northern Taiwan and has one of the few outdoor sea life amphitheaters in Taiwan. The facility features an indoor aquarium and outdoor show that is geared toward children.  

Hours:
Yehliu Geopark: 8 AM to 5 PM in winter (tickets not sold after 4:30)
8 AM to 6 PM in summer (tickets not sold after 5:30)
Yehliu Ocean World: 9 AM to 5 PM

Price:
Yehliu Geopark: 80 NT per person.
Yehliu Ocean World: 330 NT per person (children are sometimes free)
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Can I touch the rocks?
Don't you dare touch the rocks! 

How to get there:
​By Bus: There are inter-city buses that leave hourly from Taipei Main Station and Taipei City Hall to Yehliu. 
By Car/Scooter: Take Provincial highway 2 west out of Keelung, and keep going until you reach Wanli. The turnoff to  Yehliu comes right after Wanli beach. 

Map:
Please see below: