Gibraltar is a tiny British colony lying on the southern coast of Spain. With its strategic location on Strait of Gibraltar that links the North Atlantic Ocean and Mediterranean Sea, Gibraltar was reluctantly ceded to Great Britain by Spain in the 1713 Treaty of Utrecht. Gibraltar is a narrow coastal lowland bordering the Rock of Gibraltar, known in myth and legend as one of the two Pillars of Hercules set up which marked the edge of the known world for the ancient Greeks and Romans. The Upper rock can be reached by cable car and offers magnificent views of North Africa and the meeting of the Atlantic and Mediterranean Oceans. Other highlights are St Michael's Cave, a dramatic natural grotto which forms a magnificent auditorium for classical music concerts and the historic Siege Tunnels, a honeycomb network of tunnels covering some 32 miles built for defence in the late 18th century. Gates and fortifications are a constant reminder of Gibraltar's military past and a Moorish castle dates back to the 11th century. Along the coast there are a number of rocky and sandy beaches popular with holidaymakers.