A visit here is a journey to the heart of UK democracy. Officially called the Palace of Westminster, the Houses of Parliament's oldest part is 11th-century Westminster Hall, one of only a few sections that survived a catastrophic fire in 1834. Its roof, added between 1394 and 1401, is the earliest known example of a hammerbeam roof. The rest is mostly a neo-Gothic confection built by Charles Barry and Augustus Pugin for 20 years from 1840. The palace's most famous feature is its clock tower, officially the Elizabeth Tower but better known as Big Ben.

Big Ben is actually the 13.5-tonne bell, named after Benjamin Hall, who was First Commissioner of Works when the tower was completed in 1858.

At the business end, parliament is split into two houses. The green-hued House of Commons is the lower house, where the 650 elected Members of Parliament sit. Traditionally the home of hereditary blue bloods, the scarlet-decorated House of Lords, with almost 800 members, now has peers appointed through various means. Both houses debate and vote on legislation, which is then presented to the Queen for her Royal Assent (in practice, this is a formality; the last time Royal Assent was denied was in 1708). At the annual State Opening of Parliament, which now takes place in May, the Queen takes her throne in the House of Lords, having arrived in the gold-trimmed Irish State Coach from Buckingham Palace (her crown travels alone with equerries in Queen Alexandra's State Coach).

Visitors are welcome on Saturday year-round and on most weekdays during parliamentary recesses (which includes Easter, summer and Christmas). They can choose either a self-guided audio tour (adult/child £18.50/7.50) in one of eight languages lasting about 75 minutes or a much more comprehensive 1½-hour guided tour of both chambers, Westminster Hall and other historic buildings conducted by qualified Blue Badge Tourist Guides in a myriad of tongues. Afternoon tea (£29) in the Terrace Pavilion overlooking the River Thames is a popular add-on to the tours. Buy tickets from the office in Portcullis House on Victoria Embankment. Tour schedules change with every recess and are occasionally subject to variation or cancellation due to the State Opening of Parliament and other parliamentary business, so check ahead and book. UK residents can approach their MPs to arrange a free tour and to climb the Elizabeth Tower.

The public entrance to the Houses of Parliament is St Stephen's Entrance, housed within St Stephen's Tower.