1. The Hal Saflieni Hypogeum is an underground prehistoric burial site located in the city of Valletta, Malta. It was discovered in 1902 and is believed to have been in use between 4000 BC and 2500 BC. The site is made up of a complex network of underground chambers, passageways, and tombs, with some areas being over 10 metres deep. The hypogeum features intricate carvings and paintings, including the famous \"Sleeping Lady\" statue. It is considered one of the world’s most important archaeological sites and is a UNESCO World Heritage Site.

2. The hypogeum is open to visitors by guided tour only, with tours limited to 10 visitors at a time. Tours must be booked in advance and can be arranged by calling +356 2182 7011. Operating hours are from 9am to 5pm, Monday to Sunday.

3. Tickets cost €35 for adults and €16 for children, with discounts available for students, seniors, and groups. The hypogeum is located in Paola, a short distance from Valletta, and can be reached by public transportation. Bus lines 81, 82, 90, and 280 serve the area. Parking is limited, so it is recommended to use public transportation or a taxi.