The long time home of the British monarchy, Buckingham Palace is a massive, stately structure that is one of London's most popular tourist attractions. Visitors enter through the mall, which is home to the Victorian Memorial (a nautical sculpture of Queen Victoria), and are able to enter a number of state rooms on guided tours, all of which are decorated in the most regal furnishings, while also displaying some amazing pieces of art from the Royal Collection (think Rembrandt, Poussin, and more).
Other highlights include the largest private gardens in London, the artifacts of the Queen's Gallery, as well as famous routines like the daily changing of the guard at 11:30am.
Note:The cheapest, most basic tours available cost 18 GBP ($28 USD). For up-to-date info on when certain tours or ceremonies are available to the public, consult the included website.