Algar Do Carvão

The Algar do Carvão is one of the most unusual natural sights in the Azores, a vertical volcanic chimney on the island of Terceira that can be entered and descended. It lies inland from Angra do Heroísmo, in the high ground of the island's centre, and from the outside it is not obvious: an opening in a grassy slope, surrounded by ferns and trees, with no hint of what lies below. The word algar means a cave or pit, and carvão means coal, a reference to the dark colour of the rock.

The cavity was formed when a volcanic vent emptied of its lava, leaving a hollow duct that rises from deep underground to the surface. After the lava drained away, the roof of the chimney remained open, and over time the walls cooled and hardened. Visitors descend through an artificial tunnel of about forty metres, built to make access safe and easy, and then a series of steps and platforms inside the cavity. The chamber is huge, almost ninety metres deep from top to bottom, and its walls rise in rough, dark curves, streaked with colours from red and orange to green and black, where minerals and algae have stained the rock. Silica stalactites, formed by water seeping through the lava and leaving white deposits, hang from the ceiling and walls.

At the bottom, around fifteen metres below the visitor platform, lies a small, clear lagoon of rainwater, which varies in depth through the year. Light enters through the opening high above and falls in a shaft through the dark, and on a bright day it makes dramatic beams and shadows. Dampness and silence give the place a cathedral-like atmosphere. The walls above the platform are covered with ferns and mosses near the opening, creating a contrast between the green vegetation at the top and the dark rock below.

The site is open to visitors on a limited schedule, usually in the afternoon, with longer hours in summer, and guided entries are the rule, so check times before going. The steps are wet and can be slippery, and the temperature inside is cool and damp, so wear shoes with grip and a jacket. A helmet is usually provided. The visit takes around an hour, including the descent.

It suits families with older children, geology enthusiasts, and photographers. Combine it with Angra do Heroísmo and the walk on Monte Brasil for a full day on the island.