Coba is an ancient Mayan city just outside of Tulum. It was once one of the most powerful Mayan cities in the Yucatan, now reduced to ruin by time and nature, but it is certainly an interesting area to explore. Some people rent bikes to get around the ruins, but our group felt more than comfortable walking around. In fact, I think it would have been much more difficult on a bike, as the roads were not paved and the area was hilly. The main attraction on the site is Nohoch Mul, a giant Mayan pyramid, one of the only of it's size and kind that you can still climb to the top of. The steps leading to the top were very steep, not meant for someone afraid of heights. By the time you reach the top you are high above even the tallest trees, and you can see for miles in any direction. Other smaller, but no less interesting ruins surround this giant spectacle, including a game court where opposing teams would try to get a rubber ball through stone hoops. It's written that the losing team would sometimes be sacrificed. Losing the game could mean losing your head! Just imagine playing a game with those kind of stakes! This little outing only took about a half a day, and we did it during the same weekend that we went diving in the cenotes. My only tip here is not to plan it in the middle of the day because it does get super hot. We were lucky enough to have an awesome taxi driver that took us to get drinks and snacks on our way there, and had a cooler of ice for us to leave them in. He waited around for us while we explored the ruins so we had nice cold drinks to come back to in the end. It was very resonablely priced too, but that was probably because we had such a large group. Just outside of the site there are a few restaurants that serve really yummy food and ice cold drinks. It's a little over priced of course, but what do you expect at a tourist attraction.