Chichén Itzá ruins -
The Chichén Itzá ruins were about a 3 hour drive for us via Tulum ( we rented a car ) ... OK I got lost for a bit! Make sure to get a tour guide as they'll tell you many interesting facts.
Make sure you climb the big pyramid ( 91 steps! ) - don't bother with the inner pyramid, it's just a sweathouse in there and not very interesting.