Exit the airport and take the Federal Highway 307 south towards Playa del Carmen and Tulum. Continue on the Federal Highway until you reach the stop light at the edge of Tulum (approximately 110 km) and turn left towards Boca Paila/Punta Allen.
Continue approx 3 km and the road will "T", bear right (south). Continue 5-6 more km thru the Tulum Hotel Zone, Casa Carolina will be on your left and is located immediately past La Valise Hotel. If you reach the entrance to the Sian Ka'an Biosphere (an Arch over the road) you have gone about 1 km too far.
Travel time from Cancun airport to Casa Carolina Tulum is approximately 1.5 hours.