A huge iceberg – glistening, green and translucent – has incongruously floated into Manchester city centre. This is Urbis, Manchester's £30m millennium project and the culmination of the city centre's phoenix-like rebirth after the devastation of the IRA bomb in 1996. Due to open in June, it has been designed by local practice Ian Simpson Architects.

Sheathed in its shiny, smooth skin of green-tinted frameless glazing, this freestanding, highly sculptural form changes spectacularly with each viewpoint. To the Arndale shopping centre, it presents a sharp prow six storeys high. Towards Victoria Station, beyond the opposite end, its roof sweeps down like a ski-jump and is finished in pre-patinated copper that perfectly matches the green-tinted glass walls. On Corporation Street, a sheer glass wall rises straight off the pavement. On the other side, towards the cathedral and a new terraced park, the main building sprouts a single-storey wing that embraces the main entrance.

Urbis, meaning "of the city", is billed as a new kind of museum that tells the story of cities through the experiences of its inhabitants. A novel diagonal glass lift glides visitors to the fourth floor from where they trickle down through the exhibits. The fifth and sixth floors house a restaurant and bar graced by a spectacular rooftop panorama of the city centre.

The glazed external walls are made up of narrow, alternating horizontal strips of clear and translucent sand-blasted glass. They offer views in and out of the buildi ng, underlining the connection between the museum's theme and the surrounding city. As Ian Simpson explains: "The building is itself part of the city experience it exhibits."