Nautilus

This vessel at first appears to be a Gargantuan sea monster 230 feet long by 30 feet in height and width, its body covered in hard reflective scales. Along the top there is a hidden catch, which can be found with a successful DC 23 Intelligence (Investigation) check. Releasing the catch unlocks a hatch revealing a cylinder wide enough for a Medium creature to crawl inside. The Nautilus is a Gargantuan object with the following statistics:

Armor Class: 25
Hit Points: 400 (damage threshold 20)
Speed swim 200 ft. (can turn a maximum of 15 degrees in a round)
Damage Immunities poison, psychic
Crew Capacity 25; Passenger Capacity 600
Travel Pace 58 miles per hour (460 miles per day)

To be used as a vehicle, the Nautilus requires one pilot at the helm. While the hatch is closed, the compartment is airtight and watertight.

The steel submarine holds enough air for 15,000 hours of breathing, divided by the number of breathing creatures inside (at most 625 for 24 hours). There are 2 decks of interior compartments, most of which are 6 feet high. Interior doors are airtight, have AC 20 and 50 hit points, and can be bypassed with DC 18 Dexterity (thieves’ tools) checks or DC 25 Strength checks.

The Nautilus floats on water. It can also go underwater to a depth of 9,000 feet. Below that, the vehicle takes 2d6 bludgeoning damage per minute from pressure.

A creature at the helm can use an action to pilot the Nautilus by making a DC 18 Intelligence (vehicle [water]) check, with disadvantage if there are no other creatures controlling the ballasts, hydraulics, and sensors (each an action), or with advantage if each position has a creature helping. On a success, the pilot can double the effects of any acceleration, deceleration, or turning they make with the Nautilus on their turn. In addition, the pilot can send the submarine careening into a creature or object, making an attack roll as usual.

Prow. Melee Weapon Attack: +12 to hit, reach 20 ft., one target. Hit: 34 (8d6+6) piercing damage. On a natural 1, the Nautilus takes 34 (8d6+6) bludgeoning damage.

Any creature in the command room can pull a lever to activate its function, but the Nautilus only responds to the first 8 levers pulled in a round, and a lever only performs a function once per round. While traveling forward the lever to travel backwards does not function, and while traveling backward the level to travel forwards does not function. After each use, a lever goes back to its neutral position.