What are the must-do and see things while we're there?
It depends a lot on what are you looking for. If you're looking for nightlife and party then you should go to Calle 12 where are all the bars and nightclub located.
If you're into swimming with turtles, Akumal is a beautiful place where you can swim with them with no cages in between.
You might want to enjoy some history, if so: visit Tulum Archaeological Zone. It's landscape is unique in the world and also you can enjoy a day in the beach over there. Bring lots of water, though. And do not, I repeat: DO NOT skim on sunscreen. You will regret if you do.
I strongly recommend you to avoid big parks such Xcaret or Xel-ha since they're generally overcrowded, unless of course: you like the Disneyland-ish crowds.
Feel free to contact me if further assistance is required.
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Hi, here are my favorite things to do there.