Verbier Festival, Verbier, Switzerland <!-- none onestar twostar threestar fourstar -->

Set up 13 years ago, in the francophone Swiss Alps, as a way of combining world-class music with jet-set partying, the Verbier Festival has certainly proved its musical worth: it has become a magnet for serious music-lovers, and graduates from its youth orchestra take top orchestral jobs all over the world. Nowhere else do you find such a combination of stellar talent and boldly imaginative programming.

Its founder, Martin Engstroem, describes it as a "laboratory" - a concept nicely corroborated during my three-day visit. I saw China's young piano tornado Lang Lang, whose career to date has been based on solo flamboyance, tamed under the tutelage of the violinist Joshua Bell and cellist Ralph Kirshbaum, and turned into a genuine chamber player: he led them through Dvorak's labyrinthine Dumky Trio with responsive sensitivity.

And I saw a dozen other stars who normally shine alone - Nikolai Lugansky, Mischa Maisky and Julian Rachlin among them - modestly blending into a variety of chamber permutations.

But each had their moment of glory. Bell's came in a recital with the pianist Jeremy Denk, which he opened with a beautifully coloured performance of Mozart's K301 Sonata, followed by the most exhilarating Kreutzer Sonata I've heard in years. After roughening his tone for Bartok, Bell then produced a rarity, Prokofiev's Cinq mélodies, but not even Bell's art could bring substance to it. Finally, on the wings of an Ysaÿe Caprice, Bell swept us into virtuoso heaven - appropriate as we were in a church on top of a mountain.

In a concert that unfurled like a flower, the pianist Emanuel Ax led us through a Mozart programme that began with a solo sonata rendered with wonderful strength and limpidity, followed by a serene version of a violin sonata with the virtuoso Leonidas Kavakos: the climax came when they were joined by two players for a majestic performance of the G Minor Quartet.

Meanwhile, in another concert, the ebullient pianist Leif Ove Andsnes was given carte blanche to invite other stars to share the stage. Despite turning showy musical cartwheels all evening, he revealed his true excellence in two short encores.