Atlantis: Bearer of Fruit (Book 1, Part 2, Papyrus 2) starts out with a description of un underwater eatery.
The Tebeck Bridge hovered over First Mote connecting to the boardwalk. It had a little restaurant which sat in the side of its curve and was adequately named the Tebeck Crest. The stone building spiraled its way underground three levels deep where windows protruded into the underwater life of the mote. Sea horses, octopus, dolphins and mermaids swam by, ignoring the gluttonous gawkers. Flickering blue reflections bathed surrounding stone walls with coolness.
In 2008, on a trip to Sea World in Orlando, Florida, we had lunch at a restauruant called Sharks. The place offered a view of underwater sea life while you dine. I drew upon this experience when writing the first draft for the Tebeck Crest chapter.
In case you're in the Orlando area, here is the info on "Sharks" --