<P> There are a number of small gardens surrounding the Palace of Westminster . Victoria Tower Gardens is open as a public park along the side of the river south of the palace . Black Rod's Garden (named after the office of Gentleman Usher of the Black Rod) is closed to the public and is used as a private entrance . Old Palace Yard, in front of the Palace, is paved over and covered in concrete security blocks (see security below). Cromwell Green (also on the frontage, and in 2006 enclosed by hoardings for the construction of a new visitor centre), New Palace Yard (on the north side) and Speaker's Green (directly north of the Palace) are all private and closed to the public . College Green, opposite the House of Lords, is a small triangular green commonly used for television interviews with politicians . </P> <P> The Palace of Westminster contains over 1,100 rooms, 100 staircases and 4.8 kilometres (3 mi) of passageways, which are spread over four floors . The ground floor is occupied by offices, dining rooms and bars; the first floor (known as the principal floor) houses the main rooms of the Palace, including the debating chambers, the lobbies and the libraries . The top - two floors are used as committee rooms and offices . </P> <P> Some of the interiors were designed and painted by J.G. Crace, working in collaboration with Pugin and others . For example, Crace decorated and gilded the ceiling of the Chapel of St. Mary Undercroft . </P> <P> Instead of one main entrance, the Palace features separate entrances for the different user groups of the building . The Sovereign's Entrance, at the base of the Victoria Tower, is located in the south - west corner of the Palace and is the starting point of the royal procession route, the suite of ceremonial rooms used by the monarch at State Openings of Parliament . This consists of the Royal Staircase, the Norman Porch, the Robing Room, the Royal Gallery and the Prince's Chamber, and culminates in the Lords Chamber, where the ceremony takes place . Members of the House of Lords use the Peers' Entrance in the middle of the Old Palace Yard front, which is covered by a stone carriage porch and opens to an entrance hall . A staircase from there leads, through a corridor, to the Prince's Chamber . </P>

Who designed and built the houses of parliament