If you've never seen a cenote, or sinkhole (I hadn't until my first time in Mexico), then you should absolutely add one to your Tulum bucket list. There are many options and variations near (and nearish) Tulum, many of which you can swim in. As with most things in the area, the further away from Tulum beach, generally the less crowded (unless you're heading back up toward Cancún). They are inexpensive and unique sites to visit. There are even smaller ones on Tulum beach road on the jungle side! I've been paddling and swimming in one right across the street from where our rental home was. They are especially pleasant on a particularly hot day, because the water in cenotes tends to be cooler than ocean water — just watch out for caimans . . .
