We were not real thrilled with the port of Calica in general - nothing like Cozumel. We took the Tulum excursion, which was wonderful, then had a few Corona's at the port and went back on the ship a little early to enjoy some pool time before the crowds.
There are lots of taxis there to take you places, best thing to do is research on where you can go from there or book your excursion through Carnival.
Here is a link to our webalbum from our cruise last year on the Inspiration to Grand Cayman and Calica. The only pictures in the port are of all us drinking Corona!
Have Fun!