I noticed something the other day, when I was reading Harry Potter (Again!).
So, I think we're all familiar with the fact that Gryffindor is associated with Fire, Ravenclaw Water, Hufflepuff Earth (Soil) and Slytherin is of course water. Where their common rooms are has something to do with this.
Gryffindor: Fire: Their Common Room always has fires. That one was obvious.
Slytherin: Water: [i]they're under the lake![i] The lake has water, yes?
Hufflepuff: Earth (Soil): Part of their common room is [i]under the ground[i]. So if they had windows that weren't magically enchanted, they would be able...