Undertree Inn by pegahoul
"Welcome, children, to the Undertree Inn. Where you can play and party all night long, without adults to say "don't do this", "don't do that" or "go to bed". When you're tired, comfortable beds are already prepared at the second floor. Enjoy yourself, don't mind the screams you heard at night. When morning come, the caretaker will escort what's left of you to the edge of the forest. It will be an experience you'll never forget."
Half an hour sketch, 20 or so hours (5 days) of fun painting ^^.
Although it turned exactly as I wanted, I'm still not satisfied on some part. Plus, I don't know if drawing those misty dementor-ish things on the background a good idea or not, but it does support the story ^^.