London is supposed to be the most expensive city in the world, but it's still astonishing what you can get for zilch. Entrance to all of our state museums and galleries; a glass of Thames tap water; a ride on a bendy bus; and, tomorrow, any number of unique performances by some of the world's best musicians.

Exhibition Road Music Day has been bringing free music to SW7 for some years now - but this time the stops have been pulled out for a musical jamboree worthy of this refined cultural quarter. Some 400 acts, encompassing German electro, Indian classics and French jazz, will be playing in 20 different venues - from the Institut Français to the Natural History Museum. The event is part of the worldwide La Fête de la Musique, celebrating the longest day of the year, but let's not shy away from proclaiming that London has the best line-up of all the cities involved.

The blind Malian duo Amadou & Mariam are among the biggest draws, playing a set at the Institut Français at 9.30pm - and if the phrase "blind Malian duo" sounds a little off-putting somehow, you obviously haven't heard their thrilling, sun- kissed album Dimanche à Bamako, which is as funky as a dog in shades.

British Sea Power, the eccentric Brighton quintet, uphold their tradition of playing in unlikely venues by dispatching a set of indie rock in front of the dinosaur skeletons in the Natural History Museum (9.30pm).

Prince Albert, sitting on his golden perch opposite his eponymous hall, has a prime spot. A stage by his memorial will host folktronic act Four Tet (6pm); the delightful blues artist Florence and the Machine (6.50pm) and the japetastic Late of the Pier (7.40pm).

But the best tactic is to seek out the esoteric and the strange. There are numerous outdoor stages on Exhibition Road itself, which is pedestrianised for the day. Or how about Teutonic punk from MIA at the Goethe-Institut perhaps (8pm)? Or the Persian/Arabic Ismaili Community Ensemble, jamming with the Royal Philharmonic Orchestra at the Ismaili Centre? (noon and 4.30pm).

Please note that British Sea Power's gig is free but restricted; tickets are available from the Natural History Museum's Central Hall from 10am; tickets for Amadou & Mariam available at the Institut Français from 1pm; both are first come, first served.

• Tomorrow, 10am-midnight. exhibitionroadmusicday.org.