Explore the world's most top-secret swimming holes, including the mystical Fingal's Cave in Scotland which boasts symmetrical basalt columns, and an incredible limestone pool hidden from the horizon in the desert of Oman.

From a gorgeous underground lagoon on the Hawaiian island of Oahu, to an adrenaline-filled 70-foot cliff jump in California, to the most unexpected scuba dive location in the world, uncover the planet's best-kept swimming hole secrets.

From swimming with sharks in Belize, to a seaside cascade in Costa Rica, to kitesurfing in the Caribbean and four-wheeling in South Africa; thrill-seekers explore the world's most top-secret swimming holes.