Sailors avoid­ed this place for cen­turies because they believed it was haunt­ed by witch­es and mon­sters, but mod­ern tourism has since proven them very sil­ly indeed. Sun­light fil­ters into the cave through a tee­ny-tiny entrance (vis­i­tors have to lie flat in a boat to get in), fill­ing the space with a stun­ning blue light that gives the cave its moniker. Swim­ming is for­bid­den and right­ly so, but vis­i­tors to the Blue Grot­to usu­al­ly get more than enough enjoy­ment from, you know, just look­ing at it. The cave is found on Capri in the Bay of Naples.