<P> The dormitories are in Ravenclaw Tower, on the west side of Hogwarts . The common room, which went undescribed in the series until the climax of Deathly Hallows, is round and filled with blue hangings and armchairs, has a domed ceiling painted with stars and features a replica statue of Rowena wearing her diadem . Harry also notes that Ravenclaws "have a spectacular view of the surrounding mountains". A logical riddle must be solved to gain entry, whereas the Gryffindor and Slytherin common rooms only require a password (Hufflepuffs need to tap a barrel in the rhythm of "Helga Hufflepuff"), indicating that it may be easier for those students from other houses who possess a high degree of intelligence to enter this common room than others . Professor McGonagall, the head of the Gryffindor House, solves the riddle accurately . </P> <P> Slytherin values ambition, cunning, leadership, and resourcefulness; the Sorting Hat said in Harry Potter and the Philosopher's Stone that Slytherins will do anything to get their way . The house mascot of Slytherin is the serpent, and the house colours are green and silver . The Head of House is Severus Snape until the seventh book . Then, Horace Slughorn, the previous Head of House, comes out of retirement re-assuming authority after Snape becomes headmaster . The ghost of Slytherin house is The Bloody Baron . According to Rowling, Slytherin corresponds roughly to the element of water . The founder of this house is Salazar Slytherin . </P> <P> The Slytherin dormitories and common room are reached through a bare stone wall in the dungeons . The Slytherin common room is a long, low, dungeon - style room, under the Hogwarts Lake, furnished with green lamps and carved armchairs . The room is described in the second book as having a greenish glow . </P> <P> The Sorting Hat claims that blood purity is a factor in selecting Slytherins, although this is not mentioned until the fifth book . There is no reason to believe, however, that Muggle - born students are not sorted there, merely that pure - blooded students are more desirable to that house, as there are several examples of half - bloods in the house (such as Snape and Voldemort). In Deathly Hallows, a group of Snatchers claim that "not many Mudbloods" are sorted into Slytherin . </P>

What are the meanings of the four houses in harry potter