Try scuba diving in Tulum. The best dive sites in the region are located off the island of Cozumel, some distance away. But what you can do in Tulum that you can't off Cozumel is dive in Cenotes. Cenotes are underwater connecting caves found all around Tulum. As Tulum receives far less visitors than its northern neighbors, you will often have the cenotes to yourself. Dive only with a scuba shop certified by one of the major dive organizations such as the Professional Association of Diving Instructors. The cenotes in this area will not have the reef life you will see off Cozumel. However, the draw here isn't fish, it's the caves themselves. Often times you will swim in between huge, hanging stalactites as you make your way with a flashlight from one cenote to the next.
Drive just outside of Tulum to the Punta Laguna Nature Preserve. Punta Laguna was created by a local Mayan family who still have a say in its operations. Guides here are surprisingly knowledgeable about the flora and fauna but not all of them speak English. Pay for a guide and your certain to see monkeys as they use radios to track them. The preserve sits in an area of virtually untouched, dense rain-forest. Look for Howler and Spider monkeys in the trees. Wildlife is plentiful here and you can expect to see our friends in the forest without cages. You will usually see a variety of bird and insect life, including butterflies. Be warned that if you have mobility issues this isn't the best choice of activity --- the ground here is often quite wet and full of stones and roots.
Explore the Mayan ruins by the sea. The biggest tourist draw in the town is the ancient Mayan city of the same name. This city played a major role as a trade hub between both land and sea from as early as 600 AD. The ruins today consist largely of buildings that made up the town center: ceremonial and administrative structures. Most of Tulum's Mayan citizens lived just outside this area in houses made of wood and palm. Refresh yourself by diving into the cool waters below. Fortunately for you, the ruins sit right on top of the ocean. As the temperature rises, don't resist the temptation to strip to your bathing suit and dive into the sea. But while you're there, remember that this very cove was once the port for many ships delivering goods from central Mexico to Central America.
