You come to the Riviera Maya for water and ruins. On the coast, Playa del Carmen's Quinta Avenida is the main walking street, with shops, restaurants and street performers, and the ferry from its pier runs out to Cozumel in about 45 minutes — Cozumel has some of the best shore diving and snorkeling in the Caribbean. Further south, the Tulum ruins sit on a bluff directly above the sea and can be visited in a morning. The inland city of Chichén Itzá, the most famous Maya site in the Yucatán, is a long day trip by car (about 2.5 hours). The quieter Cobá ruins, in the jungle 45 minutes from Tulum, still let you climb the main pyramid.
Away from the ruins, the region's main attraction is its cenotes — flooded limestone sinkholes connected by underground rivers, ranging from open swimming holes lined with tropical forest (Gran Cenote, Cenote Azul) to cathedral-like caves that you can snorkel or dive through. The eco-parks Xcaret, Xel-Há and Xplor package a sanitised version of the same experience with zip lines, dolphins and buffet lunches; purists will prefer to hire a car and find the quieter cenotes along the jungle roads inland. The Sian Ka'an Biosphere Reserve, south of Tulum, is the best place in the region to see manatees, dolphins, and wading birds in something close to their natural state.