Just in case anyone's interested, here's what I ended up doing. (The PCs were level 3, by the way.)
I ran a scenario based around this puzzle that I found on YouTube:
The party was traveling and the vampires were getting hungry, so when they spotted a settlement up ahead, they expected to be able to snack on some villagers. However, when they got there, they found the place deserted. They followed a trail into the woods, where they found a ruined castle with the obelisk in the center. The necessary items for the statues were in chests scattered about the ruin. (I was able to borrow some terrain for this part, which the players really liked.)
Once they solved the obelisk puzzle, it sank into the ground, exposing a staircase leading downward. At the bottom of the stairs, two dire wolves guarded a door leading into a huge underground laboratory. In the lab, a mad scientist was brewing up some kind of experiment, with the villagers in cages waiting to be his test subjects. He had a tentacled abomination (stats of a gelatinous cube) for a bodyguard. The PCs saved the villagers and then bit a few of them.