Hufflepuff basement

"It is round and earthy and low-ceilinged; it always feels sunny, and its circular windows have a view of rippling grass and dandelions. There is a lot of burnished copper about the place, and many plants, which either hang from the ceiling or sit on the windowsills. Our Head of house, Professor Pomona Sprout, is Head of Herbology, and she brings the most interesting specimens (some of which dance and talk) to decorate our room – one reason why Hufflepuffs are often very good at Herbology. Our overstuffed sofas and chairs are upholstered in yellow and black, and our dormitories are reached through round doors in the walls of the common room. Copper lamps cast a warm light over our four-posters, all of which are covered in patchwork quilts, and copper bed warmers hang on the walls, should you have cold feet."

- Gabriel Truman

The Hufflepuff Basement serves as the common room for students in Hufflepuff house at Hogwarts School of Witchcraft and Wizardry. In general, it sports several motifs, such as circles, nature, copper and the colours yellow and black (all associated with the house of Hufflepuff). It also emphasises comfort, said to be "the cosiest common room of them all". It is at one floor below the ground and is very sheltered from the elements, generally allowing students to sleep easier than those in the towers (like Gryffindor and Ravenclaw).

Entrance
The entrance to the common room is located "in a nook on the right hand side of the kitchen corridor", concealed behind a stack of barrels. In order to reveal the entrance, no password is required. Instead, one must tap the barrel two from the bottom, middle of the second row, in the rhythm of ‘Helga Hufflepuff’, which will make the lid swing open, exposing a passageway that will lead to the basement when crawled through. However, if the wrong lid is tapped or the wrong rhythm is used, the intruder will be doused in vinegar and barred access.

Common Room
The actual basement itself is round, earthy and low-ceilinged, welcoming, warm and sunny. There are lots of yellow hangings, burnished copper, and overstuffed sofas and armchairs upholstered in yellow and black, and circular windows that provide a vista of "rippling grass and dandelions". The head of house, Pomona Sprout, also teaches Herbology and as such brings many interesting plants in to decorate the common room (some of which dance and talk), placing them on the windowsills or having them hang from the ceiling, encouraging interest in Herbology (and hence part of why Hufflepuffs tend to be good at it). There is also a large, honey coloured, wooden mantelpiece with carvings of badgers on it. This is located underneath a portrait of the house's founder, Helga Hufflepuff.

Dormitories
The Hufflepuff dormitories are also located in the cellar and have perfectly circular doors, with lots of little underground tunnels leading off from the common room. One of them leads to the girls' dormitory, the other to the boys'. In each dormitory four-poster beds covered in patchwork quilts. The dormitories are illuminated by warm copper lamps, and copper bed-warmers hang on the wall, in case of cold feet.

Behind the scenes

 * The Hufflepuff Basement was the only common room that Harry Potter did not enter at some point.
 * Indeed, the Hufflepuff Basement is the only common room that has not been seen by non-Hufflepuffs for over a thousand years at least, making it the most secure of them all.
 * JK Rowling had previously described the entrance to the Hufflepuff common room as being close to the kitchens, the entrance of which is behind a still life painting of a bowl of fruit; one must tickle the pear for access (see Harry Potter and the Goblet of Fire). This is consistent with LEGO Harry Potter: Years 1-4. Pottermore states that the barrel reveals a passageway — through which one may crawl to the common room.
 * On Pottermore.com, if a player gets sorted into Hufflepuff, a new chapter, written by J.K. Rowling, will be unlocked and enabled to read, describing the common room in full detail.
 * Hufflepuff is the only house that also employs a repelling device against intruders (they are doused in vinegar should the pass-rythm be wrong) as opposed to simply barring access.
 * The Hufflepuff Basement is the only common room that is decorated with vegetation.

Appearances

 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Deathly Hallows
 * LEGO Harry Potter: Years 1-4
 * Pottermore