More than seven million people, from six continents, are crammed into this heaving metropolis, creating one of the largest cultural mixing pots on earth. This is where the money that drives the British economy is made and spent, where the Queen reigns and parliament governs, and where trends in music, fashion and the arts are made and discarded, sometimes in the space of a single evening.
In a changing London with the run up to the 2012 Olympics, you will still see all the clichés - red buses, black taxis and bobbies on the beat - but you will also find improved infrastructure, reinvigorated public spaces and some of the best nightlife, shopping, theatre, music and dining in the world. Here are ten of the best London experiences.
1. "Off with their 'eads!"
The castle founded by William the Conqueror in 1078 found a new use as a prison. Dozens of heroes and rogues were locked up or beheaded inside the Tower of London, from Sir Thomas More and Sir Walter Raleigh to Guy Fawkes and Ann Boleyn.
Do not miss the Crown Jewels, perhaps the most ostentatious collection of baubles in existence, or the gruesome armoury of medieval weapons in the White Tower, or the Bloody Tower, which stills contains graffiti scratched into the walls by former prisoners. The cheerful Yeoman Warders (Beefeaters) lead free tours around the castle daily.
2. One powerhouse of architecture...
Thousands pose for photos in front of the Houses of Parliament and their famous clock-tower, Big Ben, named for the giant bell inside. Across St Margaret's St is Westminster Abbey, where British monarchs have been crowned ever since 1066, and where a dozen former kings and queens are buried. Close by is the famous black door of Number 10 Downing St, occupied by the Prime Minister.
3. ...And another architectural masterpiece
Emerging from the ashes of the Great Fire of London and surviving the firestorm of the Blitz during World War II, St Paul's Cathedral still gleams inside and out. Head straight to the vertiginous Golden Gallery atop St Paul's famous dome, reached by 530 winding steps. En route, explore the open-air Stone Gallery (378 steps) and the acoustically brilliant Whispering Gallery (259 steps) inside the dome. In the crypt are tombs and memorials to the greatest heroes of the British Empire - Nelson, Wellington and Churchill.
4. Great works of art within a work-of-art
Housed in a stunning conversion of the power station that once supplied the city with electricity, the Tate Modern is the world's most popular modern art gallery. The focus is on well-known modern names, like Picasso, Mondrian, Pollock, Lichtenstein and Mark Rothko. Stand-out works include Francis Bacon's Triptych, Max Ernst's Celebes, Alberto Giacometti's spindly figurines and the excellent collection of Russian propaganda posters.
5. The green lungs of London
In 1808 the parliamentarian William Windham declared that Hyde Park should be preserved at all costs as the "lungs of London". Good thing, too. Along with London's other Royal Parks, Hyde Park is a national treasure. Together, these open spaces make London (surprisingly) the greenest city in Europe, and Londoners love the parks as places to picnic, sunbathe, observe wildlife, see bands, play sport and even demonstrate against the government.
6. Cruise the Thames
Passengers on the river already get a grandstand view of all of the above, the maritime precinct at Greenwich and the garden of office towers at Canary Wharf. Half a dozen companies offer transfers along the river, from chugging commuter boats to the zippy shuttle service between the Tate Modern and Tate Britain. With time to spare, you can even ride the river all the way to Kew Gardens or Hampton Court Palace.
7. Greenwich mean time
Green and pleasant Greenwich is the precise location from which global time and points of distance around the east-west axis of the earth are measured. These things are not so important in the digital age, but back when Britain depended on its navy for its wealth and its power, a few degrees out here or there could spell disaster - as happened in 1707, when the British fleet sailed too close to the Scilly Isles and 1,400 perished.
As well as the historical attractions, people come to Greenwich for the feeling of escape from the big city. Greenwich was - and still feels like - a village, and the backstreets are lined with interesting and quirky shops.
8. The world's a stage
Londoners first got the theatre bug in the 17th Century when Shakespeare and his contemporaries starting performing comedies and dramas for the masses on the stage of the original Globe Theatre. Four hundred years later and Londoners are still obsessed with the stage. Theatre-land in the West End around Soho and Covent Garden boasts more than 50 theatres, staging everything from period romps and big-name musicals to occasionally cringe-worthy shows based on banging dustbin lids and rap poetry.
9. Find treasures in the British Museum
Founded in 1753 to house the personal collection of Sir Hans Sloane, the museum was dramatically extended in the Georgian period, and the central Grand Court was covered by a soaring geometric canopy by Sir Norman Foster in 2000.
Inside you can see such historical wonders as the Rosetta Stone and the controversial Elgin (Parthenon) Marbles, swiped from the Acropolis by Britain's ambassador to the Ottoman Empire. The collection of Egyptian mummies in rooms 62 to 63 is legendary.
10. Old masters and familiar faces
The National Gallery and the neighbouring National Portrait Gallery fill in all the gaps in the history of painting that are not covered by the Tate Modern and Tate Britain. These grand neoclassical monuments house some of the country's finest paintings and, refreshingly, not all are stuffy 17th-century oils - there are wacky modernist works and cartoon caricatures as well.
The article 'Lonely Planet's top 10 outings in London' was published in partnership with Lonely Planet.