Torca del Carlista
Torca del Carlista is a large limestone cavern found in Cantabria, Spain, approximately 35 kilometres (22 mi) from the city of Bilbao.
The entrance, up the slopes of the Cantabrian Mountains, is only a single metre wide. The entry passage descends some 45 metres (148 ft) vertically in a narrow chimney before opening up into the cavern's main gallery. Some 520 metres (1,710 ft) long and 245 metres (804 ft) wide, the total surface area of the cavern exceeds 20 acres, or 76,620 square metres (824,700 sq ft). The main chamber is the fifth-largest underground chamber in the world, with a ceiling that reaches 120 metres (390 ft) at its highest point.
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