London ? London isn’t one of the world’s bargain destinations, and the feeble U.S. dollar makes it all the more daunting for American visitors.

But it’s possible to have a day out for less than a “tenner” — a 10-pound note, now worth about $19.

Start with the free attractions: the British Museum, the National Gallery and National Portrait Gallery in Trafalgar Square, the vast and fascinating Tate Modern gallery across the Thames from St. Paul’s Cathedral, the Imperial War Museum, the Victoria & Albert Museum, the Natural History Museum and the Science Museum. Those are the best-known among the capital’s 200 or so museums and galleries. Most museums also will have special exhibitions that do charge admission.

There’s no charge for watching the Changing of the Guard at Buckingham Palace, which happens daily at 11:30 a.m. from April through the end of July, and every other day the rest of the year.

Admission also is free for the Ceremony of the Keys at the Tower of London at 9:50 each night, but you need to plan ahead. (Visitors may request up to seven passes by writing to: The Ceremony of the Keys, H.M. Tower of London, London EC3N 4AB.)

A cheap but vanishing essential of any London visit is a ride on one of the double-decker Routemaster buses; they’re the ones with the open platform on the back and a conductor waiting to sell a ticket. The fare is just 1.20 pounds, or $2.25, for a single ride; you also can get an all-day London Transport ticket, which includes Underground trains, for 4.70 pounds, about $9.

If you fancy shopping, London boasts a variety of markets selling everything from fresh fish to vintage jewelry. Take a trip on the Central line tube to Liverpool Street for a day at Petticoat Lane market, and trawl through the vintage clothing.

Pretend you are Eliza Doolittle and roam through the old and new in the Covent Garden market, and catch some of the street performers.

Many say the best way to view London is by foot. Walking tours are a popular way of catching the hidden details, and the guides have a wealth of knowledge.

Two elements that epitomize London are British Telecom red phone boxes and the double-decker Routemaster buses. Travelers on a budget can take advantage of the buses, as the fare is just 1.20 pounds, or .25, for a single ride.

Scare yourself on a Jack the Ripper walk or relive Shakespeare’s London. Original London Walks offers 100 routes at 5 pounds each — about $9.40. For the same price, London Mystery Walks offers the Jack the Ripper walk and the Haunted London walk.

The National Theatre on the Southbank offers the Travelex 10-pound season, when two-thirds of the seats are available for a tenner or about $19.

Web sites such as www.lastminute.com may have some theater tickets for the same price.

The Tricycle Theatre, one of London’s better-known small theaters, offers 30 to 50 tickets for Tuesday and Saturday matinees on a “pay what you can” basis. This offer is available to students, seniors and people with disabilities. The theater also offers some “early bird” tickets for less than 10 pounds or $19.

Rail lines serving London offer a range of “two for one” deals. Attractions taking in part in the promotion include the Royal Botanic Gardens at Kew, HMS Belfast, Dali Universe, Tower Bridge Exhibition and The London Aquarium. Typically you have to produce a train ticket and a voucher from the Web site — www.london2for1.com — to qualify.