Foster’s most visionary projects have arisen out of his collaboration and friendship with Buckminster Fuller. In 1971 they designed two bubbles that never materialised, a subterranean theatre and a total environment office that inspired Willis Faber; and in 1982 the two architects again worked together, on a geodesic dome dwelling that also failed to be produced. The following year – 10 days after delivering the speech at Foster’s RIBA Gold Medal ceremony – Fuller died, and Foster had to wait until 1989 to undertake another futuristic project in the vein of the American master. The opportunity arose with a colossal off-shore commercial development for the Japanese Obayashi Corporation. Foster proposed a conical tower rising up to 840 metres and 170 storeys (twice the height of the world’s highest building), bound in a helical steel grid, and holding offices, shops, hotels and flats. With a faint resemblance to Wright’s Mile High project, and echoes of Archigram’s urban fantasies, Foster’s Millennium Tower is a sound engineering project in the tradition of communication towers, but also a haunting social utopia – a community in a precinct, rising out of a marina in a virtual vertical island – so it is difficult to avoid ambiguous feelings about the abandonment of the project...[+]