Geomunoreum

Geomunoreum is the source. Around three hundred thousand years ago it erupted and the lava that poured north-east from it hollowed out as it drained, leaving the Geomunoreum lava tube system - Manjanggul, Bengdwigul, Gimnyeonggul, Yongcheondonggul and others, among the finest lava caves anywhere and the reason Jeju's volcanic landscape was inscribed by UNESCO in 2007. The cone itself is forested, with a deep horseshoe crater, and the walk is a guided loop of a few kilometres taking two to three hours through dense evergreen and deciduous woodland, past charcoal kiln sites and Japanese-dug tunnels from the colonial period, with the crater and the tube system explained on the way. Access is deliberately restricted to protect it: numbers are capped, visits must be booked in advance, guides lead every group, it closes on Tuesdays, and turning up without a reservation does not work.

What you actually see

• The horseshoe crater - the forested cone at the centre.
• The tube-system explanation - where the lava ran and what it left.
• The forest walk - the guided loop through dense woodland.
• The old kiln sites - charcoal workings and tunnels in the wood.

When to go

April to June and September to November. Book well ahead - daily numbers are capped, and it closes on Tuesdays.

Honest expectations

No reservation, no entry - this is enforced. Visits are guided and follow a fixed route at a set pace, largely in Korean. The lava tubes themselves are separate sites, and most are closed to visitors entirely.

Nearby

Manjanggul lava tube is open to visitors nearby; Bijarim and Sangumburi are close.