You can easily go to the ruins of Coba from Tulum. Coba is 50 km. northwest of Tulum, and its beauty lies in the fact that the ruins are located in the jungle. Go to the Tulum Crucero to wait for buses, colectivos, and taxis to Tulum. The buses go only several times a day, so check as to the hour at the bus station in town. You can take the bus from the station. We took a taxi for the same price as the colectivo would have cost the three of us. We got there fast, but held onto our seats as the taxi raced down the dirt road. It was not a comfortable ride. Since there are only a couple of return buses and the bus does not originate in Coba, you may be standing for the 45 minute ride back to Tulum.
You reach the village of Coba before seeing the entrance to the ruins, but it is a short and easy walk. There are many very inexpensive restaurants and hotels there. The archeological sight is open from 6 a.m. until 6 p.m. and there is an admission charge except on Sundays when it is free. Be prepared to walk several kilometers on foot in a jungle-like area with lots of mosquitos and other insects. We paid a guide because we always learn more that way, but the guide is expensive and I'm not sure it's worth it for these ruins unless you can share the fee with others. Buy a book and do a self-guided tour.
Dress for the heat and humidity-bring a lot of water. There are men on bicycles with carts attached who will drive you to certain locations for a fee. You can also rent a bicycle. Plan to spend at least two hours at the site. The main attractions here are the Grupo Coba, the ball court, Nohoch Mul and the Great Pyramid. This is the tallest Mayan structure in the northern Yucatan.
After leaving, stop at El Bocadito, which serves as Coba's bus terminal. You buy bus tickets here, but I would suggest buying them before you enter the ruins so you can check the schedule and make sure there is room on the bus. We arrived and had to wait two hours for the bus and then had to stand the entire way back. The owner here is very friendly and will give you a lot of free advice. The restaurant food is basic and good and very cheap. They have a vegetarian platter.