Although the ruins of Tulum are not spectacular, the setting is. The majestic cliff top ruins overlook vast stretches of beach and turquoise water. You can swim here and that is the best part. As you swim below you look up at the splendid Mayan Ruins and the sight is impressive. There are many little coves and beaches and private spots. To best enjoy the ruins go early in the morning or in late afternoon when the tour buses aren't there. It is free on Sunday and that is when the Mexican locals go.
Tulum was occupied from 1200 - 1521 and was a walled city. Its strategic function was that of a fortress. The city was abandoned about 75 years after the Spanish conquest. Tulum's tallest building is a watchtower fortress overlooking the Caribbean named "El Castillo". When you take the bus to Tulum, make sure you tell the driver to let you off at Las Ruinas, the town is another couple kilometers away. Then you must walk about half a mile to the ruins, or you can take a train-like shuttle but you have to pay and the walk really isn't long. The heat is oppressive though in the middle of the day. Thunderstorms come up quickly and there is not much shelter when you are viewing the ruins. Last time we took protection down by the water under some cave-like formations.
We go back to the ruins of Tulum time and time again because of the beauty.
The Mayan Palace arranges tours but you can easily go on your own. You can take the Mayab bus to Playa del Carmen and then transfer to another that will take you to Tulum, or you can take two colectivos (white vans that you flag down). Tulum is a little down the road from Xel-Ha but spend a day at each as you will want the entire day at Xel-Ha. After you finish at the ruins, take a taxi to town( fares are posted everywhere and are regulated) and eat lunch or dinner.