If you're not Korean, or don't live in the region, you might not be familiar with Jeju Island. Basically, it's Korean Hawaii. Super popular for honeymooners, lots of beautiful sights and fun activities. It's located just south of the Korean Peninsula, and is a quick plane ride from Seoul, but with a nicer climate.
I visited in the off-season as it was late November and a bit chilly. Kind of like the weather in San Francisco. After dropping my luggage off with the hotel, I hired an English speaking taxi driver for the day and did a tour around the eastern part of the island.
One of the places to visit is the Sangumburi Crater (산굼부리), the flat crater of an extinct volcano. Technically, it's a maar (마르) crater, and the only one in Korea and thus designated as Natural Monument #263 by the government.
Elevation: 1,367 ft
Field around the Sangumburi Crater on Jeju Island, South Korea.