The Broader Picture: A guide to invisible London

The Great Bear is young London artist Simon Patterson's double-take on the London Underground map. First shown in 1992 at the Hayward Gallery's 'Doubletake' exhibition, it is now an icon of Nineties art - a baffling non sequitur, ordinary and strange, funny-odd and funny-ha-ha, brow-furrowing and groovy all at the same time. You certainly couldn't use it to get from A to B, but it seems to suggest you might make your journey more interesting if you did. It asks fascinating questions about modern reality. For example: did Wittgenstein actually have any connection with Westminster? Efforts to look for patterns quickly collapse in the face of the realisation that every station on the Circle Line is named after a philosopher.

There is one destination for which this map might be perfectly suited. Between Harpo Marx and Sid James on the Comedians Line is an empty warehouse building on the edge of the City which has been chosen as the location for 'Seeing the Unseen', a new exhibition of contemporary art. The 21 works on show, including The Great Bear, come from an 'invisible museum' that until now has existed purely in their anonymous owner's head. This is the first time its works have been brought together as a public display; usually they are scattered about in the homes of trusted temporary guardians. The idea of an invisible museum is inspired by the 1949 book Musee Imaginaire by the French critic Andre Malraux - unseen on The Great Bear.

'Seeing the Unseen' is made up of works that other museums might have been reluctant to buy, since although they are all by established and well-known artists, they are often works made at stages in the artists' careers during which they were trying out something new. The shadowy collector of these bits and pieces talks about London as one big fragmented museum. He has selected and arranged the works to emphasise urban themes. These relate to the present, even though the works come from different times and circumstances.

A mass-produced madonna by Katherina Fritsch, a photo of a Michelangelo-esque male nude by Robert Mapplethorpe and a painting of a Japanese gizo death doll by Adam Lowe combine to suggest a contemporary altar-piece theme. Damien Hirst's 1991 drawing for his shark suspended in formaldehyde, The Impossibility of Death in the Mind of Someone Living, meets Yves Klein's photo, The Void, of 1960, showing the artist making an apparently fatal leap into the street from a top floor window. Other artists whose work can be seen here include Matthew Barney, Richard Long and Rachel Whiteread.

'Seeing the Unseen' is an effective model of art now, with its loose connections, its idea- and image-association, a constant return to the everyday, but in altered states - the feeling that you've been there, you know what's happening, but you're not quite sure how the artist is making it happen. In that sense, the invisible museum might stand in relation to a conventional museum in much the same way that Simon Patterson's Great Bear stands in relation to the conventional map of the London Underground. Where exactly is the art in The Great Bear? Is it the concept or the execution? Is it twisted and cunning or just stunningly literal? Is it about words or places? How many days would pass before you were sure you'd read every name on the map?

'Seeing the Unseen' is an eccentric, decidedly mind-over-matter experience. It's an on-the-run show, too. See it quick before it disappears.

'Seeing the Unseen' is at 30 Shepherdess Walk, London N1, noon to 5pm, until 2 October (admission free). Matthew Collings's film 'A Real Work of Art?' will be on 'The Late Show', on BBC2, next month.

(Photograph omitted)