For the past couple of days I've had random urges to read old books I can't remember the names of.
One in particular I read maybe 10 or so years ago. It was a kid/teen book and I'm really fuzzy on the details. I only remember that at one point, the protagonists (1 male, 1 female, both teenage) are in an underwater room or cave with a mural on one of the walls. The male protagonist is partially trapped in a tank with a pufferfish at the other end, and I think he kicks his way out? There's also something about a lot of pressure (like the bends) and the mural shattering when a door is opened in the room, relieving the pressure.
Sorry I can't recall more detail on this, it was pretty much half my life ago :)