The Royal Sea Scope isn't quite a submarine, but it's the next best thing for anyone who'd rather stay dry: a glass-bottom boat with a lower observation deck where wide underwater windows frame coral reefs, shoals of tropical fish and, often, a diver feeding the fish just outside the glass. It's a short, gentle trip that suits everyone from toddlers to grandparents, with an optional stop to swim or snorkel from the boat if you'd like. Transfers and a guide are included.