Off the coast of Andros, the largest island in the Bahamas, lies an alien world waiting to be explored. Under the waves exist over 200 underwater cave systems known as “blue holes” that offer a window into the distant past.
Deep in Bulgaria's wondrous karst landscapes lies a natural wonder that has captivated travelers for ages. Prohodna Cave, the country's largest tunnel-like cavern, features an unearthly pair of symmetrical holes in its lofty ceiling known as the "Eyes of God."
Perched dramatically in the mouth of a 400-foot cliff in southwest Slovenia is Predjama Castle, certified by Guinness World Records as the world's largest cave castle.