1. Tate Modern and Tate Britain
These exceptional art galleries, situated on the south and north banks of the River Thames respectively, house some of the finest artworks in the world -- from Picasso to Monet to Warhol -- yet they don't cost a penny to visit (except special exhibitions).
Wander around the exhibitions at your own pace, or join in one of the free daily guided tours, where a knowledgable guide will enlighten you about international, contemporary and British art.
Find out about Saga's Art Appreciation holidays
2. Queen Mary's Rose Gardens
A wonderful escape from the bustling city centre, these stunning, quintessentially English gardens, situated in Regent's Park, are home to one of the finest collections of roses in the country.
There are almost 400 varieties in all, some with wonderful names such as 'Lovely Lady' and 'Thinking of You'. Don't miss the focal point of the garden, the Rose Wheel – a series of ten planted beds that radiate out from a focal bed, surrounded by benches set into alcoves formed by climbing roses.
Find out about Saga's Garden Holidays
3. Changing of the Guard
Time it right and you can witness one of the world's greatest spectacles without taking your wallet out of your pocket.
Get you camera ready as the new guard arrives – wearing his iconic tall bearskin hat – at the forecourt of the Palace at 11.30 (daily from May until the end of July, and on alternate days for the rest of the year – see royalcollection.org.uk for details) from Wellington Barracks, accompanied by a band, before the ceremony is conducted on the Palace forecourt, and the old guard returns to the barracks.
4. The South Bank
From the London Eye and Globe Theatre to Millennium Bridge and Southwark Cathedral, it's amazing how many landmarks you can see along this stretch of the River Thames without paying a penny.
Top tip: download a free walking tours of the South Bank area, which explore "intriguing pockets of architecture and history" along the Thames.
Find out about our exclusive Saga discounts on London hotels
5. Evensong at Westminster Abbey
While the 700-year-old Abbey relies on admission fees from visitors to cover running costs, it never charges people who want to worship.
Visit during Evensong, arguably the most beautiful of services where the Abbey choir sings, which takes place at 5pm on Mondays, Tuesdays, Thursdays and Fridays, plus at 3pm on Saturdays and Sundays. It's a wonderful way to experience the Abbey in the way it was intended -- as a place of worship and reflection.
6. Museum Of London
It is astonishing that this great museum – the world's largest urban history museum with a staggering 1.1 million objects – is free for visitors, considering you could spend a whole day there. The collections, which range from prehistoric times to the present day, are constantly changing.
You can view everything from artefacts of pottery, bone and stone that were recovered during dredging operations in the Thames in the 19th century to clothing by London-based designers, including Vivienne Westwood. There are some brilliant temporary exhibitions too.
Related: The best museums in London
7. Foyer concerts at the National Theatre
Fancy tapping your foot along to some free jazz? Head to the Djanogly Concert Pitch, in the foyer of the National Theatre, early evening on a weekday (pre-performance) or at lunch time on a Saturday, and you can do just that, thanks to a series of free concerts.
The range of music is exciting and varied, including trumpet-led jazz bands, violin and piano duets, swing bands and even ukulele and guitar duets.
Find out about Saga's Music and Jazz holidays
8. British Library Tour
The British Library has to be one of the world's greatest libraries -- ever wondered about the techniques used to care for the vast collections? Join a free 'behind the scenes' tour of the studios in the Centre for Conservation.
Led by British Library conservators, they give an fascinating insight into the techniques and methods used to care for the collections (booking recommended).
9. Borough Market
Located in a vast open-air space under a Victorian-style warehouse roof, this is London's oldest food market (more than 250 years old) and has to be one of the best in the world.
Arrive early, on a Thursday, Friday and Saturday and while away the morning sampling your way around the endless stalls.
What can you expect? Everything from fresh seafood and cured meats to pies, ground coffee, ales and homemade cakes (look out for the brick-sized brownies, they are out of this world).
10. Sir John Soane's Museum
This amazing house at Lincoln's Inn Fields was designed by the great Sir John Soane, architect of the Bank of England, to live in, but also as a setting for his antiquities and works of art.
Free to visitors, it houses over 30,000 architectural drawings (including both drawings by Soane and those by earlier and contemporary architects that Soane collected), antiquities, Neo-Classical sculptures and works by Hogarth, Turner, Canaletto and Piranesi.
Saga readers can save an extra 10% on all SuperBreak's to London. Visit the SuperBreak website for more details.
Do you have a favourite free London attraction? Tell us in the comments below.