Red Lake is a sinkhole filled with water near the town of Imotski and Blue Lake. The name comes from the solid red cliffs at the edge of the lake. It is believed to be one of the deepest lakes in Europe. The last depth measurement was performed in 2013 when 255m was measured. The lake is probably connected to other waters via a cave 280 m at its bottom. The lake was thought to have formed when the ceiling of a large cave hall collapsed. Unlike Blue Lake, it cannot be reached, but it is viewed from the top and is not dry, so it can be visited all year round.