Sangumburi Crater is the crater of an extinct volcano. Unlike its brethren Halla-san and Songsan Ilch'ubong, this one exploded quickly, but did not spew much lava nor did it form much of a surrounding cone. This phenomenon is called maru in Korean, and Sangumburi is the only one of its kind in the country, making it Natural Monument #263.
The remaining crater is 100 meters deep and an average of 350 meters across. Over 400 species of plants and animals live inside the crater. Visitors can walk around part of the rim (the rest is private property and fenced off), but they cannot venture down inside the crater.
A well-paved path leads from the parking area to the viewing area which has a small pavilion and several vista points. Also on the grounds are numerous grave sites made in traditional Jeju fashion: a wide, trapezoidal stone wall surrounding the burial mound.
Several of the sites also have small stone figures that guard the mound from evil spirits. At the park entrance are several large rocks from the crater. During the eruption, molten rock flew from the volcano into the air and cooled into many exotic shapes.