We went on a tour to Tulum through our resort the Aventura Spa Resort. It was a great tour. What a great place to visit and the history in the place is amazing.
Make sure to go on a tour because I don't think you would get as much out of it just walking around by yourself. It is much more interesting with someone explaining what is what.
The ocean view from on top of the cliffs is amazing. It is one of the most beautiful I have seen.
Make sure to wear light clothing because it is very hot in June. The ocean gives a nice breeze and there is a little beach you can swim at. There are some little shops on the way in so you might want to grab a water.