Traveling in a medium-sized cavern with high ceilings, the party hears a crash and splash ahead. Then a second one. Two umber hulks were burrowing overhead when they fell into the cavern and begin attacking the party. The party killed one and the second one fled.
The party came across a whirlpool about 50 feet across. They had to power through, with good navigation in order to get both keelboats past it to the locks on the other side.
In the huge cavern below the whirlpool the party came across a large ship, seemingly empty. Turns out it was a duergar ship with some drow passengers. The groups parted ways after a tense standoff.