Orientation -- About 45 minutes south of Felipe Carrillo Puerto, a few kilometers past the town of Limones at a place called El Cafetal (there's a gas station before the turnoff), you reach the clearly marked turnoff for Mahahual and Xcalak. It's 50km (31 miles) on a good paved road to the coast at Mahahual. The turnoff for the new road to Xcalak comes 2km (1 1/4 miles) before you reach Mahahual, at a military checkpoint. Xcalak is 55km (34 miles) to the south, less than an hour's drive.
Information, Please -- Good, up-to-date information about the Costa Maya is still scarce, though you can get decent overviews at www.mahahual.com and www.xcalak.info. For the latest goings-on, sign up for the detailed and gossipy newsletter from Mayan Beach Garden in Mahahual.