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 1394–1401, is the earliest-known example of a hammerbeam roof. The rest is mostly a neo-Gothic confection built by Charles Barry and Augustus Pugin (1840–58).

The palace's most famous feature is its clock tower, Elizabeth Tower, aka Big Ben.

Ben is actually the 13.5-ton bell, named after Benjamin Hall, who was 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 763 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 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 in Queen Alexandra's State Coach). It's well worth lining the route for a gawk at the crown jewels sparkling in the sun.

On Saturdays year-round and on most weekdays during parliamentary recesses including Easter, summer and Christmas, visitors can join a 90-minute guided tour of both chambers, Westminster Hall and other historic buildings conducted by qualified Blue Badge Tourist Guides in seven languages. Afternoon tea in the Terrace Pavilion overlooking the River Thames is a popular add-on to the tours. 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.