Try to see London well after the hubbub of the 2012 Olympic Summer Games has faded away. That way you can see the most of the city without battling so many crowds.
A Friendly Experience WALK: 2 HOURS Heathrow's not all bad if you amble down to Terminal 5. Eat fish cakes at Plane Food, a restaurant owned by Gordon Ramsay (of Kitchen Nightmares fame) with a floor-to-ceiling runway view. The queue at immigration might allow a jaunt to the Sofitel. Talking with travelers from who-knows-where at the Icelandic-style bar called Sphere is a micro-cultural experience.
See the Real London TAXI: 4 HOURS It's a pretty easy — and worthwhile — cab ride out to Marylebone, one of London's “villages” and a prominent locale in Sherlock Holmes stories. If there's such a thing as old English ambience, this is it. The 18th-century architecture always makes me think I'm in a well-heeled country town. On a nice day, grab lunch to go at a nearby cafe and then eat under an old tree at the vast Regent's Park. Souvenir tip: Buy the beautifully packaged soaps in Ortigia before cabbing it back to the airport.
The Walk of Fame TRAIN, WALK: 4 HOURS Take a 15-minute sprint on Heathrow Express into Paddington. Then two stops on the Tube into Notting Hill. Yes, that Notting Hill. Stroll the two-mile Portobello Market, graze on some cheese and pick up an antique decanter.
Airport or Here? TRAIN, TAXI: 4 HOURS An eight-hour layover is pretty common in London. It's also an opportunity to see in one afternoon the half-dozen iconic sites (like Big Ben) that some people plan an entire vacation around.
Best Pic of the Trip TAXI: 6 HOURS Head to Windsor Castle, the world's oldest and largest occupied castle and an official residence of Her Majesty the Queen. If it's April through July, get here by 11 a.m. to see the changing of the guard.
A Dish to Talk About Later TAXI: 6 HOURS Given a fat wallet I'd book lunch at the Fat Duck just west of Windsor. Its innovative combinations (think snail porridge and jelly of quail) have earned it the U.K.'s Best Restaurant award for three straight years. Mind you, at $240 per person for the tasting menu, perhaps it's just as well that you forgot to make a reservation.
England in Your Face TRAIN, TAXI: 8 HOURS Within an hour of the airport you can be in Westminster at the foot of Big Ben. This is iconic London, with Parliament on one side and the Thames River under your nose. I'd cross the Millennium Bridge and turn along the South Bank, passing the London Eye and Tate Modern before heading back across the bridge.