El Soplao (Cantabrian: El Soplau) is a cave located in the municipalities of Rionansa, Valdáliga and Herrerías in Cantabria, Spain. It is considered unique for the quality and quantity of geological formations (speleothems) in its 17 miles length, 6 of which are open to the public. In it are formations such as helíctites (eccentric stalactites defying gravity) and curtains (draperies, or sheets of calcite, sometimes translucent, hanging from the ceiling). Its formation dates back to the Mesozoic, in particular the Cretaceous period 240 million years ago.