Walking through this collection of the shortlisted entries from the annual Koestler Awards scheme offers privileged access to the invisible subconscious life of more than 200 depersonalised residents of prisons, young-offender centres, psychiatric hospitals and immigration removal centres.

The works - many of them anonymous - are inspiring, amusing, skilful, mournful, profound and often breathtakingly ingenious, constructed with limited materials, including paper and card, clay, matches (an unimaginably fiddly crane and containers), carved soap, false nails (gorgeous miniature paintings), and a meticulous origami samurai killing dragons. Most commercially brilliant is the Monopoly game set in Lewes Prison.

Everyday reality is understandably less popular than escapism; an exquisite drawing of Dartmoor's exercise yard bursting with tension contrasts with C Dyer & D Mewell's inmate watching TV on his bed. The anonymous Futility and Depression, a self-portrait from Dartmoor, is an important reality check. Home, an iconic sleeping figure wrapped in blankets on a pavement, constructed from recycled card, makes a link with institutional life. Fleeing reality leads to beautifully executed cartoon stills, holiday memories, and zany, fantasy animals (Demented Pheasant).

A bowl inspired by Grayson Perry is an incongruously lyrical tribute among the many crafted works (a postage-stamp collage of Bob Marley, two Daleks, a papier-m‚ché dog from Holloway, painted and embroidered hangings, which include "Black History") reflecting the insider populations.

This annual event is always a unique opportunity to experience the creative energy exploding behind bars. Unmissable.

Until 9 September. Information: www.ica.org.uk, www.koestlertrust.org.uk; 020 7766 1404.