Trou aux Cerfs is one of Mauritius's most accessible natural wonders — a perfectly formed dormant volcanic crater sitting in the middle of the highland city of Curepipe, 550 metres above sea level. The crater is 109 metres deep and roughly 200 metres in diameter, and its almost geometrically circular shape gives it an otherworldly perfection when viewed from the rim road.

The crater was formed by a phreatic eruption — a steam-driven explosion caused when rising magma superheated groundwater. It last erupted more than 700,000 years ago and is now classified dormant, with no volcanic activity expected. The interior is filled with dense tropical vegetation — a self-contained miniature forest visible from the paths around the rim.

A paved road circles the entire crater and is used by joggers and walkers, making it a popular morning exercise spot for Curepipe residents. The views from the rim are among the finest on the island on clear days — the central plateau stretches out in all directions, and when the clouds lift you can see both the east and west coasts simultaneously. The weather at altitude is noticeably cooler and damper than the coast — Curepipe is sometimes called "the city under the clouds" — so bring a light layer.

The crater itself takes about 30 minutes to walk around at a comfortable pace. There's no charge to visit, and parking is available on the roadside. Combine with a visit to Curepipe town, which has several colonial-era buildings, a busy market, and the good Telfair shopping mall if you want coffee and air conditioning. The crater is at its most dramatic in low cloud, when the mist rolls across the rim and the forest below disappears into grey.