Maelstrom: Sarissa would explain that the party is welcome to explore more of the palace first and understand this is prolly their first time under the sea. However, some of the other giants here (especially her sisters) are not to be trusted. The party will need to be stealthy or think of a good cover story.
Airship: The airship's enormous balloon is made from dragon
hide that has been dyed bright red. Atop the balloon is
a crow's nest that is reached by crawling up the ropes
on the outside of the balloon. Crawling up the ropes
requires a DC 10 Strength (Athletics) or Dexterity (Acrobatics)
check. If the check fails, no progress is made; if
the check fails by 5 or more, the creature falls.
The balloon is roped to a gondola that has been fitted
with steel runners. The airship has a speed of 8 miles
per hour while skiing across ice or snow or flying in the
air. A strong headwind reduces the ship's speed to 4
mph, while a strong tailwind increases its speed to 12
mph.
By changing altitude, the ship can use air currents
to move in a particular direction. A propeller aft of the
gondola thrusts the ship forward and can also be pivoted.
The hull of the gondola is watertight and buoyant
in water, and the propeller can push it across water.
The airship can hold up to 1 ton of cargo and requires
a crew of two, one to operate the propeller and one to
operate the furnace. If the ship has fewer than two crew
members on duty, its speed can't be controlled, and it
moves in a random direction, carried by the wind, until
control is regained or until it collides with something.
The gondola and the balloon are separate targets.
The gondola has AC 13, 250 hit points, and a damage threshold
of 10. The balloon has AC 11 and 50 hit points. Both
have immunity to poison and psychic damage. If the balloon
drops to O hit points, it bursts, and the ship loses
the ability to fly. While the balloon or gondola has at
least 1 hit point, it can be repaired. Repairing 1 hit point
of damage to either the balloon or the gondola requires
1 day and costs 20 gp. (Mending spells can repair superficial
damage but can't restore hit points.