Presented by the Roma sotterranea association, a group of urban speleologists (also known as urban archaeologists), allow you to explore the Last Frontier" underneath Rome. Any large, long-inhabited city such as Rome always has some underground structures like catacombs, sewers, and aqueducts. In addition, in part the result of quarrying to obtain building materials and in part due to the growth of the city, hypogeums or underground chambers have formed under Rome. While some areas of the Roma sotterranea Web site are for members only, the Underground site's list includes entries on about 30 points of interest under Rome. Each entry includes a lengthy description, pictures, information on the hours open and if special permission is needed to visit, and a reservation form for booking a guided tour. Also at the Web site are maps of ancient and modern Rome, information about the organization and how to join, and a chat area for communicating with urban speleologists worldwide.