What the actual fuck?
The walls and ceiling of the room are a massive aquarium filled with sea life, from the green & leafy kind, to the toothy and bitey kind. It is not immediately apparent, but players who observe closely will be able to make out passages in this aquarium which lead out and away–presumably to the sea. The glass walls are not reinforced with magic, but rather, with remarkable feats of structural engineering. So while the glass is quite tough and won’t be shattered with a single blow from a hammer, it’s still possible to break it using mundane means. If that occurs, this room, and likely the entire dungeon, will flood.
The only horizontal entrance to this room opens onto a small 10x10ft alcove in the wall. If players step to the edge, they will see that the actual floor of the room is roughly 15 feet below where they are now. A wooden bridge long enough to reach the deck of the ship hangs from a crane on the ceiling. Unfortunately, it’s currently about 20ft higher than the surface of the entrance platform, and the lowering mechanism can be plainly seen on the deck of the ship, near the wheel.
The floor of the room has been painted blue, and is covered in dozens upon dozens of slits which run parallel to the ship. From these slits, massive 5ft diameter saw blades rise and fall in a rolling pattern, with each blade rising from its slit only after the one before it in line has reached its apex and begun to recede. This creates the image of a rolling sea of steel blades. By studying the pattern of movement, a player could easily run across the floor safely. However, at best they’d only have one chance to climb up the sheer 15ft side of the wooden boat before they were reduced to bloody chunks by the sea of steel.
The ship itself does not appear unusual in any way, save for its location here in the dungeon. There is a wheel for steering, a deck, masts with sails which are currently tied. The floor of the room has a “pocket” in it, shaped particularly so as to keep the ship upright. I have refrained from populating the ship, as there are simply too many interesting possibilities. I personally like the idea that someone wealthy and powerful created this room simply to use the ship itself as an office or dining hall, with kitchens and stores below decks. It might also serve as an excellent treasure chamber, or prison. I leave the specifics up to you.
One thing I will note is that while the entrance is the only horizontal way into or out of the room, there are two vertical exits. One is a trapdoor on the ceiling just above the main mast. It can be seen easily by anyone who looks up, as it stands in contrast to the aquarium. The other is a trapdoor in the bowels of the ship which leads to a room further down. This trap door is not secret, but it is concealed by barrels full of grog.