Gommak Sikdang

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.

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.

Geomunoreum

The volcanic cone that made the caves on this side of the island: lava from here ran about 14 km to the coast and left the Geomunoreum Lava Tube System behind it. In front of the cone a collapse trench runs about 2 km long, 80 to 150 m wide and 15 to 30 m deep, thought to have formed where cave roofs fell in. There are three routes of different lengths, two of which may only be walked with a guide. Eleven departures a day, fifty people each, and booking closes at 17:00 the day before.

Secret Forest

A walk through cedar west of Andol Oreum, with tickets sold from a mint-coloured truck at the entrance. The unpaved loop takes about half an hour and has eight marked spots to photograph, with a stand of hinoki cypress partway round. Closures are posted on the operator's Instagram rather than following a fixed calendar, which is worth checking before driving out here.