On our first Wonder cruise, we went to the Blue Lagoon Beach day. You don't have to do much of anything besides lounge on the beach or in the shade, and eat lunch. They have music, games, swimming, snorkeling and other water activities, but you don't have to participate. I like the idea of doing something "beachy" as long as you traveled all the way to the Bahamas. They have some showers to get wet under to cool off, if you don't want to get in the ocean, there really is no walking at all, except from the ship to the boat dock, and on our last cruise, there was a bus waiting (both ways) to take my parents and anyone else who couldn't walk far.
On our last cruise (with my parents, ages 73 & 70) we took the catamaran sail and snorkel. They didn't snorkel, but they really enjoyed the ride. We were back from the sail before noon, and we came back from Blue Lagoon on the early boat, which I believe was 1:30. Still had time to shop a little in Nassau.
I've heard there is way too much walking at Atlantis, and on most of the other tours, and besides, like I said, why go to the Bahamas to see a big hotel and casino?