Tulum, te Amo
Tulum is a town about two hours south of Cancun that has a hippie-chic, eco-friendly, laid back vibe. An old seaside port for the Mayans, it has beautiful white sand beaches and the turquoise waters of the Caribbean Sea. When you get too hot on the beach, head to the otherwordly cenotes. The town is changing fast as yoga resorts and spas pop up, where you can try beachside yoga classes or a Mayan sweat lodge called a temazcal. The pueblo is the main part of the town, and that's where a lot of restaurants, bars, and souvernir shops are. Walk off of the main road a little ways to get more authentic, better restaurants.
Getting here: Take an ADO bus from Cancun. It'll drop you off in the Tulum Pueblo (kind of the main street). Alternatively, take a collectivo from Cancun to Playa del Carmen, then another collectivo from Playa del Carmen to Tulum. Rent a bike while you are here (some hostels offer them for rent, but I got mine from iBike Tulum).
See: The main sight in town is the Mayan ruins in the Tulum Archaeological Zone, which are dramatically beautiful as they overlook the Carribean Sea. These ruins are a bit more, well...ruined, than other Mayan ruins in the area due to the sea salt eroding the stone. If you are looking for some more intact ones that you can climb up, try nearby Coba. Try to go early in the morning (open 8am-5pm) since it fills up fast with busloads of tourists. The bonus? Take the steps down to the small beach you can only get to through the ruins and spend your time sunbathing on the beach while looking up at the ruins.
Do: Snorkel or scuba in the cenotes. Cenotes are amazing ancient limestone sinkholes and very unique to this region. The Mayans thought their rain god, Chaac, lived there, and it's not hard to imagine why. They're cool, fresh water and it's a great escape from the hot sun as you swim into the dark caves. Swim along with schools of fish and turtles. Read more about them here until I can do an entire post on them. Follow the signs to Coba along the Boca Pailla road and the road in that direction has about five cenotes. Gran Cenote is well worth your time and the entrance fee, but Dos Ojos on the way to Playa del Carmen is not to be missed.
Stay: I stayed at Quintana Roots Hostel as a cheap option relatively close to the beach, but there is also Tulum Bike Hostel, which is right by the ruins. You can also rent a little cabana for decently cheap, or go all out and get one of the resorts on the beach.
Eat: I actually did a good bit of cooking for myself in the hostel kitchen, but I can tell you where to drink mojitos :) I had a great time at Batey's, which is in the pueblo and has the iconic Volkswagen Beetle mojito maker out front, and Papaya Playa Project, which is along the beach.