Fingal’s Cave, Staffa, Scotland
A sea cave on the island in the Inner Hebrides (western archipelago) of Scotland is formed by hexagonally jointed basalt columns within an ancient lava flow (similar to Giant’s Causeway in Northern Ireland). The cave is known for its natural acoustics; thanks to its size and cathedral-like arched roof, the waves echo inside, producing eerie sounds. To access the cave, you can take a local sightseeing cruise to the entrance.
The Great Blue Hole, Belize
About 60 miles off the coast and part of the Belize barrier reef, the Great Blue Hole is an underwater sinkhole that’s home to a number of distinct species of fish and other marine life. Encircled by an island of coral, it has a rich blue color and is close to 1000 feet wide and 400 feet deep—it’s believed to be the largest sinkhole in the world. Snorkeling and diving in it are popular, and it can also be seen by flight.