Well, there were so many, but I would say that my wife and I going parasailing at the same time was awesome! Swimming in the underground rivers of Xcaret was fun, and eating great seafood sure didn't hurt, either.
On Valentine's Day on our honeymoon we went on a jazz/lobster cruise during sunset, which was real nice.
There is so much to do for every age.
Quick Tips:
Bring snorkeling gear with you. Be ready to haggle at the markets, taxis, etc. Take a waterproof camera with you.
Don’t be afraid to use the bus. It is safe, clean, and cheap and runs 24 hours.
DON’T exchange money at the airport! Use exchange places in the mall or just withdraw from your ATM card.
Watch out for anything that’s free!!! It usually that means a timeshare sales pitch. Now, if some restaurants offer free drinks with meals, that’s okay...
Best Way To Get Around:
Go by bus, foot, and taxi if you have to! When you arrive at the airport, don’t let their "aggressiveness" intimidate you! We avoided all that chaos and went to the right and caught a coach bus. It’s about a person. We had taken it before to Cancun and to Playa del Carmen. Seriously, those taxis will rip you off!
If you have to take a taxi, take it from the street, not as you stroll out of the Hyatt! That just screams at them, "Come, rip me off!"