The third trip included a coach ride back to X-Caret for a Sea Trek. It threw it down with rain again which we didn't mind as we were going to get wet anyway.
Our scuba diving guide showed us loads of stuff including a baby Octopus & a Sea Urchin. He had some food too that the fish went mad for. It's definitely one of the best things we've done so far. Especially for me as I can't snorkel and it's the first time I'd seen fish from that angle.