Theatre: The West End, especially the areas concentrated around Leicester Square, Covent Garden, Shaftesbury Avenue and Haymarket, is one of the world's premier destinations for theatre, including musical theatre. Covent Garden has the only Actor sponsored school in the city called the Actors Centre which also gave way to the London Acting Network, a London acting community support group. In the centre of Leicester Square there is an official half-price TKTS booth. For up-to-date listings see the weekly magazine Time Out or check the official London theatreland site. The South Bank is another area well-known for serious theatre, and is home to both the National Theatre and the Globe Theatre. London's theatre scene outside of these two main districts is known as "the Fringe".
Watch a movie: As well as the world-famous blockbuster cinemas in the West End, London has a large number of superb art house cinemas. In the summer months, there are often outdoor screenings at various venues, such as Somerset House and in some of the large parks.
Watch football: Take in a home match of one of the city's 20+ professional football clubs for a true experience of a lifetime as you see the passion of the "World's Game" in its mother country. The biggest EPL clubs in London are Arsenal, Chelsea, Fulham, Tottenham Hotspur and West Ham United. A level down finds Charlton Athletic, Crystal Palace, Queen's Park Rangers and Millwall. Many of the bigger clubs will require booking in advance, sometimes many months ahead, but smaller clubs allow you to simply turn up on match day and pay at the gate. You will be able to find a ticket to a quality football match on any Saturday during the season.
Wimbledon: Wimbledon is the oldest tennis tournament in the world and is widely considered the most prestigious. Naturally it is a regular feature on the Tennis calendar. London goes "tennis crazy" for two weeks when the competition commences in late June and early July.
Open House London Weekend: Explore many of the city's most interesting buildings
during the London Open House Weekend usually held on the third weekend of September. During this single weekend, several hundred buildings which are not normally open to the public are opened up. See website for details of buildings opening in any given year some buildings have to be pre-booked in advance book early for the popular ones!
Natural History Museum: Cromwell Road. One of the first of its kind in the world. The museum houses many permanent and temporary exhibitions covering plants, animals and geology from the worlds natural history. Of interest to most would be the permanent dinosaur exhibition. Although many displays feel dated this is an excellent museum and is always, deservedly, crowded. Free.
Winter Skating: London has a number of outdoor ice rinks that open in the winter months. Considered by some to be somewhat overpriced and overcrowded, they nonetheless have multiplied in recent years, easing congestion and increasing competition. Most charge from £10-12 (adults) for an hour on the ice, including skate hire. See the district articles for the City of London, East End and Leicester Square.
Summer Skating: In summer (and also in winter, for the more dedicated) there is also a thriving roller skating (on inline and traditional "quad" skates) scene in London, catering to many disciplines including street hockey, freestyle slalom, dance, general recreational skating (including three weekly marshalled group street skates) and speed skating. This mostly centres around Hyde Park (on the Serpentine Road) and Kensington Gardens (by the Albert Memorial). See the district articles for Mayfair-Marylebone and South West London.
Shopping: If it's available, it can be bought in London. Oxford Street, Regent Street and Bond Street, all in the West End, are some of the most famous shopping destinations in the world, but they are also just the tip of the iceberg, and many London districts and town centres have unique shopping attractions of their own.