The Hypogeum (from the Greek, meaning 'underground') is a subterranean necropolis, discovered during building work in 1902. To visit is to step into a mysterious and silent world. Its halls, chambers and passages, immaculately hewn out of the rock, cover some 500 sq metres; it is thought to date from around 3600 to 3000 BC, and an estimated 7000 bodies may have been interred here. Note that prebooking online is essential; try to book around three months before your visit.

　　The ancient workers mimicked built masonry in carving out these underground chambers, and exploited the rock's natural weaknesses and strengths to carve out the spaces by hand and create a safe underground structure. Carbon dioxide exhaled by visiting tourists did serious damage to the delicate limestone walls of the burial chambers, and it was closed to the public for 10 years up to mid-2000. It has been restored with Unesco funding; the microclimate is now strictly controlled and visitor numbers to the site are limited (10 per tour and eight tours per day).

　　A few last-minute tickets for the noon and 4pm tours are available the day prior from Fort St Elmo in Valletta or the Gozo Museum of Archaeology. A 20-minute audiovisual presentation is also available at the Hypogeum. This does not need to be booked in advance but does not include access to the Hypogeum itself. For health and safety reasons, children under the age of six cannot visit the Hypogeum.