Sleeping Shark Cave is one of Isla Mujeres' more serious north-side boat dives, built around an overhead cave profile rather than a long reef cruise. Reached by a north-side boat run from the island, it combines tunnels, swim-throughs, and a drifting feel that keeps the dive moving. Plan it as an advanced site with precise buoyancy and a calm head, because current can appear and the cave section leaves less room for mistakes. Sharks are part of the lore, but recent guides treat sightings as variable, so think reef fish, barracuda, turtles, stingrays, and eels first.