We went to Cham Island with Sea Trek Tours to do their sea walking experience.Wow.
After a boat trip to the island with a very friendly crew and guide that took about an hour and a quarter we got to do the sea walk for 20 to 25 minutes which is a hundred times better than snorkelling. You put on an air fed helmet that weighs about 35 kilos then you go down a ladder from the boat about 20 feet to the sea floor then you get up close and personal with hundreds of fish that you can hand feed and be in amongst the corals.
This trip is good for older children and older folk as I am but you have to fill in a disclaimer.
Absolutely loved it and the inclusive lunch ran to 12 courses for just 2 of us. We made a valiant attempt but couldn't manage all of it.