Allen42. There a few viewers on this board that put down Cancun. That may be because they haven't been there, or if they have, maybe they had a bad experience or it could simply be a lifestyle issue where Cozumel is more their speed. They may also get the wrong impression where they think Cancun is Spring Break every day of the year. Granted there are some times it is like that, but not as much as people might think. Cancun gets a bad rap. While some consider the diving in Cozumel better that does not take away from what Cancun has to offer. There is pleny to see and do there. We go to Cancun twice a year. Sometimes three times. In all the years we have been going, we still have not done everything we want to.
This will be a long post but since you asked...
Isla Mujeres. A small island off the coast of Cancun. A half hour ferry ride. The downtown area is made up of a few marinas, shopping, restaurants and a few dive ops. You can rent a golf cart and buzz around. There are a few nice beaches, a lighthouse and rumors of a pirate's treasure buried on the northern end. In the middle of the island is a residential area, the garbage dump, a naval base, and also Dolphin Discovery and a few theme cruises like Pirate ship or Booze Cruise. But my favorite part of the island is El Garafon which is an Eco Park. Diving opportunities on Isla Mujeres are plentiful. A few popular locations are Manchones Reef and the Cave of the Sleeping Sharks. Another is the Ultra Freeze and a few shipwrecks. Great snorkelling too.
A little beyond Isla Mujeres to the west is Isla Contoy, a Federal Nature Preserve. One of the most beautiful unspolied beaches I have ever seen in my life.
A bit of a drive west but a city rich in culture and crafts is Merida. This is a trip for repeat visitors or those who are in Cancun for an exteneded stay.
In Cancun (downtown) there is a bull ring, lots of markets and great restaurants. In the hotel zone is lots of shopping, restaurants and nightclubs. A good rainy day activity is a trip to La Isla in the hotel zone which has a shark feeding encounter. You are in an acrylic cage with cut out slits and you feed the sharks inside the interactive aquarium. You are given a snorkel, this is not a dive as you are submerged to shoulder level. Great photo ops!
A half hour south of Cancun is Playa del Carmen where you can take a ferry over to Cozumel
Further south is Xcaret, another ECO park, sister to El Garafon. Sort of commercial and man made but still a nice trip. Lazy river snorkelling, dive op at Barracuda Reef and a dinner show.
Ancient Mayan ruins are spread throughout the Yucatan. Chichen Itza is popular but my favorite by far is Tulum. The view from the cliff of tulum is spectacular. I was going to say breathtaking but that would violate the rule of don't hold your breath. There is a small but beautiful beach at Tulum. And the cenote diving is worth while which is right up the road a few minutes at Dos Ojos
www.hiddenworlds.com.mx which you can incorporate a cenote trip with either a stop at Tulum or Xcaret at the same time. Others already mentioned Xel-Ha.
Feel free to PM me, I would be more than happy to share with you a few "locals" tips. Or to tell you about more opportunities. I would however, caution you against parasailing in Cancun. I have seen parasailers smacked into the side of the hotels or into palm trees by poorly trained parasailing operators.