Howl's Moving Castle is an (arguably) ugly castle that belongs to Howl, a master wizard. But because he's one of the most powerful beings in the land, it's not recommended you tell him he possesses bad interior designing skills. He can probably maim/kill you in many different ways with his magic .
Being enchanted and all, the castle has 'legs' and can move about but it needs the power of the fire demon Calcifer to hold it together. By the looks of things it's lots of different pieces of building stuck together to make a walking contraption. The castle needs a lot of holding together, and it really isn't suprising when it falls apart and gets destroyed.
The castle's main door leads to four different locations depending on how you turn the twiddly spinner thing. There's a field in wales where Howl used to live, the seaside town of Porthaven, the royal capital of Kingsbury and the moving castle near where Sophie lived in Market Chipping.
It has been shown that with the use of magic and Calcifer, Howl can change in interior of the castle to his will. The living room is where calcifer burns, which is also a kitchen, dining room and parlour. Upstairs is a corridor and a couple of rooms which contain stuff like gold statues. There is also a balcony which is just a balcony. Sometimes Sophie hangs clothes there to dry.
Howl- wizard dude who owns the place
Calcifer- a fire demon
Sophie- young-lady-turned-into-an-old-woman (no-nonsense and good at housekeeping)
Markl- howl's apprentice
Turnip head- prince-turned-scarecrow