I suspect that one of the first things people did after they built Ur was to sit down over some barley beer and say, "You know what this place could use?" The urge to imagine our surroundings improved (often along plans of our own design) is part of human nature.

Which is not to say that dreaming is pointless. Actually, utopian thinking can let slip the dogs of imagination, transforming our understanding of our actual surroundings and suggesting paths towards better results. Critique-by-utopia is, in fact, a worldchanging tool, which is why I found visiting Future City: Experiment and Utopia in Architecture 1956 - 2006 totally invigorating.

If you can make this show at London's Barbican, go. If you can't, look for the exhibit catalog/ companion book (it's pretty expensive, so this might be a good time to resurrect that old tool, the inter-library loan). If you're interested in cities, architecture and evoking better futures for both, you're robbing yourself to miss this.

Future City covers the last fifty years of the architectural underground, an underground which ended up erupting into the mainstream, and defining the architectural cutting edge for the last decade. And, if these movements needed a motto, they could have looked to Constant Nieuwenhuys' statement that

In the circumstances we soon will live in, architects cannot be limited to designing buildings

A great many people might argue that we'd all be better off if architects would stick to designing buildings, but that's another thread altogether. The fact of the matter is that people who make buildings and spaces have taken very much to heart the idea that architecture, design and engineering have duties beyond the merely functional, and this has generally been a good thing.

More, as we stand on the edge of the greatest era of city-building the Earth has ever known (or, if the demographers are right, is likely to ever know) we should be thankful for the freedom of thought that the rebels of the late 20th Century carved out and explored. Whether it was David Greene arguing that "The house is an appliance for carrying with you. The City is a machine for plugging into" or Archigram speculating about "The next vehicle which eliminates the car," these design freaks busted loose whole approaches to thinking that now enable us to take on the task of providing urban homes for seven billion people (as we're informed we must by 2050) in innovative ways.

Which isn't to say that Rem Koolhaus and Frank Gehry have the answers. What they do now with their careers is almost beside the point. The real edge has passed into the hands of another generation of city-builders, ones who are much more interested with providing sustainable neighborhoods in emerging megacities, re-imagining the nature of place as it is informed by both biomorphic possibilities and ever-present connectivity, and looking to create design patterns that celebrate group innovation more than starchitects.

But, as Wendell Berry says, "All good work remembers its history." Knowing how these folks explored possibility in the past opens new possibility today. The future cities imagined in this exhibit may never have materialized, but their ghosts still whisper in worldchanging ears.