Tulum is about 80 miles south of the Cancun airport. Rental cars are expensive and require buying Mexican insurance. Buses leave daily from Cancun and Playa del Carmen and are a cheaper alternative.
To enter Mexico, tourists from the U.S. and Canada need a tourist card, which is good for up to 180 days. You can get one free with proof of citizenship. But remember to take your U.S. passport: You'll need it to re-enter the U.S.
The Sian Ka'an Biosphere Reserve
, about three miles south of Tulum, contains un-excavated Mayan ruins, freshwater canals, lagoons and more than 300 species of birds. Fishing tours and accommodations are available.
Tulum is the site of an ancient Mayan port city perched high on a cliff overlooking the Caribbean Sea. There's a small beach below that attracts swimmers and sunbathers. Coba, a few miles northwest of Tulum, is a larger ancient Mayan site good for hiking.
A particularly interesting attraction is a cenote (Mayan for well). It is a freshwater limestone cave with a deep, cold underground pool. The Gran Cenote, about a 20-minute drive from Tulum, features stalagmites and stalactites that make for an unforgettable scuba dive. The Sian Ka'an Biosphere Reserve also has cenotes.
Most hotels in Tulum do not have electricity after dark, so bring a small flashlight. Use bottled water for drinking, especially when visiting hot, dusty ruins.