Dance Genesis Canyon Natural History Museum, London

There is a curious thrill about being in a museum after hours, a thrill compounded by the mysterious arrival of 38 young people in pyjamas. Stephan Koplowitz, whose Genesis Canyon opened this year's Dance Umbrella festival last Saturday, makes full use of the grandeur and mystery of the Natural History Museum's main hall. The dancers gradually infiltrate the darkened hall and begin to carpet the stairs with their bodies. All wear loose clothes made of a primitive pleated metallic fabric. In selecting this extraordinary material, Craig Givens has allowed the dancers to create a chameleon-like effect as they move in and out of coloured light; orange when they rise, sea-green when they hug the treads of the stairs like a long slick of primal soup.

Singers approach from far off in the galleries vocalising Italianate gibberish like a demented a cappella combo. The yodelling trio pass through the audience and emerge into the light. Sarah Jane Morris, Barnaby Stone and Jonathan Stone are high-buttoned and frock-coated Victorian tourists. Assured and uninhibited, they loudly test the acoustic of the normally silent museum - something the regular visitor would never dare to do. Their curiosity satisfied, they saunter away ululating gaily.

Alone once more, the dancers surge into life, their arms fluttering like sea-tossed weeds on a rock. This collective movement suggests a primitive life form as if the museum's 60 million specimens were going about their private business unobserved by the casual visitor whose chief interest is in the man-made glories of the terracotta hall.

The singers rematerialise in the gallery and stand on the bridge that spans the hall, their faces bathed in the footlight glow of Simon Corder's lighting. The dancers gradually file up the stairs and round the arcade to join them, forming a bridge of song. The arc of heads and shoulders are strung across the hall like fairy lights. The dancers conclude their bizarre hymn and ebb back around the first-floor arcade, pausing so that each is framed by an archway like a Veronese trompe l'oeil.

The singers' finale takes the form of an impassioned debate conducted entirely in meaningless strings of phonemes. A bell rings. Closing time? The trio tiptoe out uncertainly, leaving the gallery to its ghosts.

The simple fluid movements devised by Koplowitz for the 38-strong troupe are not fantastically interesting in themselves but they work very well in this context. The choreographer (whose previous site-specific works have included a work set in Grand Central Station) has responded brilliantly to the space he has selected. The audience, alert and responsive after 45 minutes on their feet, were soon enthusiastically testing the hall's acoustic for themselves.

LOUISE LEVENE