I did a dive trip to Cozumel and Tulum last July. We spent 1 of the days making a day trip up to Cancun for a snorkeling trip. If you are in a family of non-divers, it's kind of a cool trip -- includes lunch, hanging out on a beach for awhile, snorkeling on a reef for awhile. But if you're divers looking for an excursion, I'd skip it, because the whale shark part of it was kind of lame.
The whale sharks are something like 45-60 minutes by boat from Cancun. That day, there were 2 whale sharks spotted, with about 50 snorkel boats, each with 10+ customers apiece. The dive boats circle around the sharks in a queue. Each boat has a DM, when it is your boat's turn, ONE customer jumps off the boat with the DM, and the two of them swim over to the sharks, hang out for 1 or 2 minutes, and then swim back to the boat. The customer and the DM climb back onto the boat, and then the boat gets back in the queue. A few minutes later, the DM repeats this process with the next customer on your boat. Hopefully, each customer gets 1-2min snorkeling near a whale shark. If you have never done any diving or snorkeling before, it might be a neat experience. For our group of divers, it seemed like a very high cost for very skippable snorkeling.
