The Hufflepuff Common Room door (the place where the Hufflepuff students spend their time and do their homework) is near the kitchens, in the dungeons. It is a quite cozy and welcoming place, not at all like a dungeon. In the room there are yellow hangings and fat armchairs, with little underground tunnels that take the students to their sleeping rooms. The tunnels have round doors like barrel-tops.
The head (ruler) of Hufflepuff house is Pomona Sprout.
Cedric Diggory dies in "Harry Potter and the Goblet of Fire" book and movie.