Mount Karthala rises 2,361 metres from the southern third of Ngazidja, its massive shield shape dominating the entire island. The trek to the summit is the signature outdoor experience in the Comoros, taking six to eight hours through tropical forest, shrub land, and bare volcanic rock. The caldera at the top — one of the largest active calderas in the world at nearly 4km wide — is extraordinary: a moonscape of lava fields and fumaroles surrounding a depression that sometimes holds an acidic lake.
The ascent requires a guide, which can be arranged through guesthouses and tour operators in Moroni. The standard route starts from the village of Boboni and climbs through cloud forest before emerging into the harsher upper zone. Night ascents to watch the sunrise from the rim are popular. Temperatures at the summit can be cold by comparison with the coast below, and rain is possible at any time. Some volcanic hazard always exists — check current conditions before ascending.