Cueva de los Murciélagos Campeche State

At sundown every evening some two to three million bats swirl up from the depths of a dry cenote, forming a tornado of fur and wings that's a surreal experience. There's only a few parking spots at the end of a small dirt entry. From there it's a 15-minute hike to the lip of the cave. Look for the bat crossing signs on Hwy 186, each about 500m from the turnoff.