Hallasan (한라산) is an extinct volcano on Jeju Island of South Korea. Hallasan is the highest mountain of South Korea. Alternate names for the mountain include Halla Mountain and Mount Halla.

The area around the mountain is a designated national park. Hallasan is commonly considered to be one of the three main mountains of South Korea, with Jirisan and Seoraksan being the other two.

The mountain is located in the centre of the island and is often taken as representing the island itself. There is a local saying stating that Jeju island is Hallasan; and Hallasan is Jeju. The mountain can indeed be seen from all places on the island, but its peak is often covered in clouds. The mountain has been designated Korea's Natural Monument #182.

The mountain is home to Gwaneumsa, the oldest Buddhist temple on the island. The temple was originally built during the Goryeo Dynasty. Like many other temples in Korea, Gawneumsa was destroyed and rebuilt in the 20th century. There is a memorial site outside the temple, remembering the victims of the civil war that took place on Jeju between 1948 and 1950. It is one of the most visited places of the island.

There is a crater lake on Hallasan. It is called Paengnoktam. There is a legend attributing the name of the lake to otherworldly men who descend from heaven to play with white deer. Depending on the season, the circumference of the lake is up to two kilometre and depth up to about 100 metres.

Trails

There are four hiking trails to the top of Hallasan:

• Kwanumsa Trail - 8.3 km
• Orimok Trail - 7.8 km
• Songp'anak Trail - 9.6 km
• Yongshil Trail - 6.5 km