Playa dives the reef that runs the length of this coast, and the current does most of the work. You drop in, drift north past the coral heads with the boat following your bubbles, and surface somewhere else — which makes it one of the easier places in the Caribbean to be a new diver, and one of the reasons so many people get certified here.
From November to March the bull sharks arrive. Pregnant females gather in fairly shallow water just off the beach, and the dive is run as a controlled, no-feeding encounter by most of the shops in town. It is the single most striking thing you can do in the water here, and it is seasonal.
Inland, every Playa shop also runs the cenotes — Dos Ojos, Chac Mool, The Pit — forty minutes down the highway. Cavern dives are open to any certified diver with a guide; cave diving needs its own ticket.
Playa is also the mainland end of the Cozumel ferry, so the island's walls are a day trip rather than a move.