Udo Island

Seongsan Ilchulbong Tuff Cone

Two separate walks share the site: a ticketed climb to the summit, 30–40 minutes of stairs, and a free coastal path around Umutgae with a much gentler gradient. The monthly closure is the thing that ruins trips — it is the first Monday, not a holiday pattern anyone guesses.

Seopjikoji

A headland running out into the sea on Jeju's eastern coast. Koji is the Jeju word for a cape; for Seopji the publisher records two readings side by side — that it describes ground said to produce men of talent, and that it comes from hyeopji, meaning narrow land. The path crosses hills of red volcanic scoria and follows low rock cliffs, and a Joseon-period beacon mound stands on the open grassland. What sets it apart from Jeju's other coastal walks is that Seongsan Ilchulbong stands in the background for most of the way round, which is why it photographs the way it does.

Bijarim Forest

Two loops split at a crossroads inside the wood. Course A is about 2.2 km of level volcanic-cinder path, 40 minutes to an hour, and takes a pushchair or wheelchair with help on the slopes; course B includes rough stone and does not. Dogs are not admitted, which separates this from most Jeju walks.

Manjanggul Lava Tube

A lava tube about 7.4 km long whose main passage runs 18 m wide and 23 m high. Roof collapses left three entrances; visitors may use only the second, and may walk 1 km in from it. At the end of that kilometre stands a lava column about 7.6 m high, said to be the largest known anywhere, and that column is also where you turn round. The operator files this cave as partly open — the other caves inscribed with it are closed to the public altogether.