The island of Capri, offshore from Naples and the towns along the Amalfi Coast, has long been a popular retreat - there are Roman ruins on the island to prove it. But one geologic feature in particular - the Blue Grotto - draws just as many visitors as the beaches and boutiques.
The Blue Grotto is a sea cave that, because of the way the light flows into the cave, appears to glow a bright blue inside. There is a tiny opening at the water level, through which you can actually enter the grotto and experience the light firsthand. It’s just big enough for a small rowboat, and even still everyone in the boat must lie down at just the right moment to get inside.
Once inside, the cave opens up and you can sit up in the boat, marveling at the glowing blue light coming from below the surface of the water. The light comes from a second (and much larger) opening below the one through which you enter, but you can’t really see that opening.