The coastline south of Tulum  loops and weaves like the tangled branches of the mangrove trees that blanket much of it. It is a mosaic of savannas, marshes, lagoons, scattered islands, and three huge bays: Bahía de la Ascensión, Bahía del Espiritu Santo, and Bahía de Chetumal.
Where it’s not covered by mangroves, the shore has sandy beaches and dunes, and just below the turquoise sea is one of the least-impacted sections of the great Mesoamerican Coral Reef.
Dozens of Maya sites have been discovered here, but few excavated, and much remains unknown about pre-Hispanic life here. During the conquest, the snarled coastal forest proved an effective sanctuary for indigenous rebels and refugees fleeing Spanish control, not to mention a haven for pirates, British logwood cutters, and Belizean anglers.
In the 1990s, Quintana Roo officials launched an effort to develop the state’s southern coast, which was still extremely isolated despite the breakneck development taking place in and around Cancún . (It has always been a famous fly-fishing area, however.)
The first order of business was to construct a huge cruise ship port, which they did in the tiny fishing village of Mahahual. They also needed a catchy name: the Costa Maya. The moniker applies to the coastal areas south of Tulum, particularly the Sian Ka’an Biosphere Reserve ; the towns of Mahahual  and Xcalak ; Laguna Bacalar ; and Chetumal , the state capital and by far the largest city in the area. Few locals use the term.
It’s hard not to be a little cynical about cruise liners coming to such a remote area, whose entire population could fit comfortably on a single ship. The town of Mahahual, nearest the port, is utterly transformed when cruise ships arrive, their passengers bellying about Mahahual, beer bottles in hand, the beaches packed with sun worshippers serenaded by the sound of Jet Skis. Then again, it’s doubtful the area would have paved roads, power lines, or telephone service if not for the income and demand generated by cruise ships.
Driving the rutted coastal road to Xcalak—an even smaller town south of Mahahual—used to take a half day or more; today, a two-lane paved road has cut the trip to under an hour. The state government has vowed to control development by limiting hotel size and density, monitoring construction methods, and protecting the mangroves and coral reef. Small ecofriendly bed-and-breakfasts have thrived, not surprisingly, and more and more independent travelers are drawn to the Costa Maya for its quiet isolation and pristine natural beauty.