Visit Croatia's Blue Cave and five surrounding islands, including Hvar, on a small-group tour by speedboat from Split. Soak up the sun, and swim in the emerald waters of the Adriatic Sea. Lunch and light refreshments are included.Your speedboat tour
Image : Climbers at the bottom of the Golondrinas cave in Aquismon Region, Mexico. The towering walls of rock range from 325 feet tall to the deepest open-air pit in the world, Sotano de las Golondrinas (Cave of Swallows), which is over 1000 feet deep.
Jacob's Well -- Wimberly, Tx: One of the most significant natural geologic treasures in the Texas Hill Country. It is one of the longest underwater caves in Texas and an artesian spring. Jacob’s Well surges up thousands of gallons of water per minute.