We went to Isla Holbox last summer, and had an amazing experience swimming with the whale sharks! John wrote about it on our
blog. I highly recommend it for anyone seeking an adventure. For me, driving is part of the adventure. Although getting to Isla was not very difficult, you will want to have a good map with you. We always take our Guia Roja atlas with us on road trips. If you're not all that adventurous or you've never driven in Mexico, you'll want to take a tour.
Stewart, I would agree with Ginger about it depending on how strong of a swimmer Ian is. I'm a very comfortable snorkeler, a certified diver, and I ain't afraid of no whale sharks. But I even got a bit nervous; my heart was really racing the first time I got in the water. You can't take your time getting into the water. You sit there waiting for the go ahead from your guide. When the whale shark is in just the right spot, you get the cue, and you jump in the water immediately and start kicking your heart out to keep up. The first time, we lost the shark right way. The second time, we kept up for just a little while. The third time, we finally got it right. We were very lucky to get 3 chances. You might only get 1 or 2 if your boat is full. But any time you get with these gentle giants is really amazing!