Classic Tourist Sights/Activites

• Ride a double decker bus anywhere - Make sure you sit on the top in the front row!
• Tower of London - Go right when it opens to see the crowds; take a Yeoman Tour if you can
• Westminster Abbey - Self-guided tour and the Diamond Jubilee Gallery
• London Eye - Great views of the city
• Abbey Road Crossing - The iconic site of the Beatles album; don't miss the graffiti on the wall outside the studio
• St. Paul's Cathedral - Combine with the Tower of London or walking to other churches in the City
• Hop On/Hop Off bus tour - Gives you a sense of the city and the top sights quickly; pack hand warmers if it's cold!
• Harry Potter Studio Tour - For fans of the movies or just any movie fan
• Changing of the Guard - Try the one at Horseguards Parade for a more intimate experience without the crowds
• Buckingham Palace - The State Rooms are open from mid-July to end-September

Museums

• Churchill War Rooms - Well-done, comprehensive museum and a fascinating behind-the-scenes look of wartime in London
• The British Museum - Visit the Rosetta Stone, Parthenon friezes, Egyptian mummies
• Victoria & Albert Museum - Unparalleled art and design museum
• Museum of London  - Terrific interactive exhibits tracing the history of London. Great for kids and adults alike.
• The Royal Academy 

Getting the Feel of London

• Canal walk near bustling Kings Cross or Camden - can make a nice loop starting from SJW through Primrose Hill (go to the top to view the city) to Camden Market and back along the canal and in to Regents Park or walk to King's Cross Coal Drops Yards to get a bite
• Catch the canal boat at Little Venice for the ride to Camden Lock
• A pint in a traditional pub and/or Sunday roast
• Walk in Hampstead Heath followed by a drink or meal at The Spaniard's Inn
• Hail a proper black cab
• Alternative London tour of East London
• Blue Badge walking tour of London (try Look Up London or London Walks)
• Professional football game - It doesn't need to be Premier League to get the feel of a game
• A walk through Notting Hill on a Saturday including Portobello Road Market
• Bike from Kensington Palace in Hyde Park all the way to Big Ben, crossing Green Park and St James’s Park. Pre-ride, get a coffee at the Italian Gardens
• Walk through Hyde Park to The Grenadier, a favorite pub 
• A walk along the South Bank from Waterloo to Tate Modern via the London Eye, the monument to the very controversial "Bomber" Harris, the Golden Hind, the place where ferrymen waited to take passengers across the Thames, the Clink, the ruins of the Bishop's Palace, Southwark Cathedral, Borough Market, The Globe and Tate Modern - plenty to do in the day, stop off or just pass by various sights, depending on your visitors appetite/interests.
• And for the VERY ambitious you can add a trip on the river on the Thames Clipper, go further to see HMS Belfast and the Tower of London, visit the Shard or cross the "wobbly" bridge to St. Paul's. You can take the tube from St. John's Wood or Hampstead to Waterloo and can take the Thames Link back to West Hampstead

Food/Drink

• Ye Olde Cheshire Cheese - Rebuilt after the Great Fire of 1666, a rabbit warren of rooms. Go to the very bottom level if you can
• Borough Market - Walk through the stalls and have the best grilled cheese sandwich at Kappecasein
• Great Indian food: Breakfast at Dishoom (eggs Kejriwal, bacon naan roll and chai), and lunch and dinner at Gymkhana, Amaya or Kahani
• English High Tea - Ham Yard Hotel (cheerful, fun, and reasonably priced), Sketch (hip and colourful with Instagrammable bathrooms), Fortnum & Mason (the classic) or Brown's Hotel (Queen Victoria's favourite)

Sightly Different

• Tour the Royal Opera House or the Royal Albert Hall
• Beefeater Gin tour - Did you know that all Beefeater gin is made in London? 
• Tour Highgate Cemetery - Book the guide on the West side to get all the interesting stories 

Further Afield

• Greenwich by boat from Westminster Pier - Visiting Greenwich Park and the Prime Meridian with a pub lunch
• Hampton Court - Home of Henry VIII with large gardens to explore as well
• Windsor Castle - An easy train ride from London, the State Apartments are open from fall to spring
• Kew Gardens - Accessible by tube or overground, one of the most extensive botanical collections in the world
• Stonehenge - You'll need a car but it's worth the trip
• A country walk - Just a short train or tube ride puts you in the country, with a pub lunch to boot
• Rickmansworth Aquadome and Ruislip Lido in Ruislip Woods Nature Reserve for nature walks and water activities

For Kids

• Museum of London  - Terrific interactive exhibits tracing the history of London. Great for kids and adults alike.
• Science Museum - Great for kids
• National History Museum  - Another great one for kids. For adults, the annual Wildlife Photographer exhibit is fantastic.
• Pollocks Toy Museum
• London Zoo - It's in our backyard so we often forget about it!

For Teens

• Tea at Sketch - Make sure you send them to the bathroom
• Madame Tussaud's - A touristy classic that's fun for teens
• Jack the Ripper walking tour 
• Thames speed boat tour - They'll be going so fast they won't realize they are actually learning about London 

Things to Skip

• Oxford Circus shopping area