The Volcanic Caves of Terceira and the Furnas do Enxofre

Pick-up is from your hotel, or from a set point in Angra do Heroísmo, in an off-road vehicle or a van, then the drive out through forest and the hydrangea fields that line the roads here. The route takes back lanes up to the Guilherme Moniz crater, at 640 metres. The two volcanic caves of Terceira are up here, and they are not the same kind of thing. Algar do Carvão is not really a cave at all: it is the inside of an extinct volcano, a chimney with stalactites, vegetation down the walls and a still pool at the bottom. Gruta do Natal is a lava tube, a tunnel left behind by magma that once ran under the surface. Holly, laurel and moss grow wherever the light reaches. The guide explains how each one was made. Furnas do Enxofre comes next, where fumaroles push sulphurous steam up through the crust. Three to four hours in total, ending back at your hotel or wherever you were collected. The order of the stops can change on the day.