Grand Cayman is a mecca for snorkeling and diving.
Climbing Dunn's River Falls can be a bit of a workout if you have leg issues. This is why you really must go with a group where everyone is helping each other in a human chain. I've done it solo, many many years ago when I was 24 and in good shape. I didn't know the 'trail' the guides used and it pretty much kicked my butt. My wife and I ventured up together in 1993 on a cruise, again without a guide. Got stuck on a big rock and had to be 'rescued' by a guide. We sheepishly joined his group and tipped him well at the top. Bring along some money in a plastic bag to tuck in your trunks to tip them. Also, the guides will take cameras from everyone and take your photos at a couple places. You can trust them. They may have a dozen or more hanging around their necks! There is an annoying local market at the top that you have to walk through to get to the buses and taxis. No way around it. But doing the falls is something I suggest to everyone going to Ocho.