We went with a tour and visited Tulum first then on the XelHa. The tour left just before closing-so going without the tour I don't think would have made a big difference. The main attraction is a spring that you enter in the jungle. You can tube or snorkel. You wind through the jungle and eventually flow out into a lagoon.
Snorkeling is good, alot of fish, but visibility is tricky.
If you float on the surface, it is fine. When you dive down, you break the plane of spring water verses salt water, and the water becomes hazy. Once you get past the plane, it's clear again. They have two places to eat, some snack bars, some real bars, souvenir shops, a hammock area, lots of chairs, and iguanas everywhere. Very beautiful setting.