Gibraltar is a large promontory of jurassic limestone, situated in the western entrance to the Mediterranean. The 5km-long (3 mile) rock contains 143 caves, over 48km (30 miles) of road and miles of tunnels. An internal self-governing British Crown Colony, Gibraltar has given its name to the Bay and the Straits which it overlooks. The town of Gibraltar is an 18th-century British Regency town built on a 15th-century Spanish town which was, in turn, built on a 12th-century Moorish town. Well worth a visit is St Michaelís Cave, part of a complex series of interlinked caverns, which is used for concerts and ballet. Another popular tourist activity is the cable-car trip to the top of the Rock, stopping at the Apesí Den on the way. Gibraltarís history as a British colony means that it can offer a large selection of British dishes as well as more international fare. The Colony has a number of discos, nightspots and a casino complex, open until the early hours of the morning.