An underwater adventure for low level characters!
As the party begins to investigate strange occurrences in town, they are lead to believe that something is amiss under the water of the local lake.
Once they have investigated the shores, the party is led to a point where a cliff face meets the calm lake waters. Beneath the lightly lapping waves, is a cave entrance. Easy enough to get into, the party simply needs to swim under, and into the mouth of the cave. Since it is filled with water, the characters will need to surface up into a large room with a small underground shore.
The cave has two pathways, Left, and Down.
Left takes the party to a collection of amphibious monsters, cave dwellers, and ultimately to their goal: The source of trouble in town. If using the Plothook from "The Depths Call," then the party will ultimately find the Cursed Wizard here. The missing child from town can be saved, Cursed to become like the wizard, or dead (Or about to be) depending on your needs.
Down, however, is a dangerous path. After walking down a short way, the ground gives out underneath the party, plunging them into the depths. A whirlwind of motion catches the party. The sinkhole eventually dumps back out on the shore. If not all of the party members fall prey, be sure not to let them know until the party members still inside the cave have reason to know that their friends are alive. One way to do this: If the remaining members advance, wait until a climactic or deadly scene is about to resolve, and cliffhanger it. Go back to the lost party member, encouraging him or her to rejoin their party. Fast Forward to the point where their ally is about to die, or the bad guy get away. Allow that Player to narrate how he helps the final scene.