You could extend this itinerary to 10 days, even 2 weeks -- it all depends on how much time you want to spend on the beach. Once you've spent a little time in that clear blue water, it's hard to pull yourself away to move inland.
Days 1 & 2: Playa del Carmen & Tulum
I recommend starting your trip in fashionable Playa del Carmen, which offers gorgeous beaches and an artsy main strip called Quinta Avenida with bustling shops, cafes, and restaurants. "Playa," as it is known locally, is the gateway to Cozumel, which makes for an easy day trip by ferry. Xcaret and Xel-Ha, two outstanding eco-parks, also lie within easy driving distance. Spend your second day in any of these tempting spots or in the ancient Maya city of Tulum visiting its beaches, ruins, and the Sian Ka'an Biosphere Reserve.
Day 3: Ek Balam & Chichén Itzá
Head for the ruins of Ek Balam, which lie north of the colonial city of Valladolid. From Tulum, take the highway to Cobá and consider stopping first at the ruins here. When you get to Valladolid, continue north on Hwy. 295 to the turnoff for Ek Balam. After climbing the main pyramid and inspecting the beautifully worked sacred doorway, head back to Valladolid for a late lunch. You can then drive to Chichén Itzá via the old highway. If there's time, stop at Cenote Dzitnup, just outside Valladolid. Continue on to the ancient Maya city of Chichén Itzá and check into a hotel in the area. In the evening, see the sound-and-light show, and then visit the ruins the next morning.
Days 4 & 5: Mérida
After you've taken in Chichén Itzá, head west to Mérida and enjoy an evening in this bustling capital city. The next day, you can further explore the tropical town, or may wish to take a side trip during the day and enjoy Mérida in the evening. Choices include the Celestún National Wildlife Refuge, where you can take a boat ride and see some pink flamingos, or the ruins of Dzibilchaltún. You might also consider visiting Progreso and Xcambó, for another good chance of seeing flamingos.
Day 6: Uxmal
No matter whether you take the short way or the long way, try to get to Uxmal by late afternoon, so that you can rest and cool off before seeing the sound-and-light show at night. Uxmal's Pyramid of the Magician is one of the most dramatic structures in the Maya world and it becomes even more intriguing when lit at night. The next morning, you can explore the ruins in more detail.
Day 7: Cancún or Puerto Morelos
This last day will necessarily include a good bit of driving. Take the short route back via Umán, then use the loop or periférico to avoid entering Mérida. After about 45 minutes, you'll see signs for the highway to Cancún. If you prefer to stay in a quiet beach location near Cancún, try Puerto Morelos.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.