How to get there? Easy just hop on to an ADO bus from Tulum to Valladolid.
Where to stay? I stayed at the cheapest hostel I could find on hostelword for just one night.
Where to eat? Lots of cheap street food. And we were lucky to be there during a huge Agricultural festival its like Perth Royal Show on steroids. They had all different farm animals, millions of silly games, rides, clothes stalls, department stalls, so much food and drink. Anything you can think of the fair had it, including live music and rap battles.
What to do? Well the obvious thing is Chichen Itza. Most people go during the day, to do a tour, clap at the bottom of the pyramid to hear the bird noises but I went at night time which is free and you get to watch a light show on the ruins. Be warned the whole thing is in Spanish, and at that point I understood nothing but it was still really cool.
Another thing to do is visit the popular cenote Ik Kil which is located on the Chichen Itza grounds, there are also other less populated cenotes that you can visit in the area.