Fly to Cancun, Mexico. The either rent a car, hire a taxi, or catch the bus to Tulum.
Head south toward Tulum on Highway 307. The entire drive will take about 1.25 hours. The highway is in excellent condition for most of the way (4 lane divided highway). The first major landmark will be a sign for Xel-Ha. There will be a HUGE Mexico flag on a hilltop right next to the highway. At this point you are about 30 minutes from the turn off.
When you see a sign advertising a restaurant on our cove called Casa Cenote, you will know you are getting close. Then you will see a large sign that says "Tankah Tres" (between highway marker KM238 and KM 237). Since there is now a divided median, you will have to go PAST this turn off less than a mile, then U-turn at the "Dreams Resort". Now you are heading north, and will need to exit to the right.
Drive toward the coast (less than a mile), until you are forced to take a 90 degree turn to the left. Follow this dirt road past the Casa Cenote Restaurant. When you see a sign that says "Slice of Paradise" tied to a palm tree (lot #55), you will know you have arrived!
Immediately take off your shoes and put your feet in the water!