One Glass House no one threw a stone at

Philip Johnson's creation, now open to the public, offers a crystal clear view of the workings of his mind

Your first thought on approaching Philip Johnson's 1949 Glass House is that it has the same problems as a very small bikini.

Would my life look good in this? Could it stand the exposure? And what kind of major reformation to my habits and vices would it take to fit into this thing?

Fortunately, it had some storage.

The house, which recently opened to the public as a National Trust for Historic Preservation site, is austere but not threatening.

It is one of the great monuments of Modernism in the US, by one of the most influential architects of the country. Johnson also defined the cleanest lines of the International Style.

The Glass House, a picture of which graces almost every book on 20th-century American architecture, was just that: a rectangular pavilion of steel supporting glass walls, with a brick 'core' that contains a small bathroom and a fireplace.

It still looks spectacular.

Restored and safe
Since Johnson died in 2005, curators have restored the Glass House's flat roof. They have obviously kept up the landscape, which is so integral to its beauty, so that the house looks just as it does in pictures, like a transparent box in the middle of a painting.

In 1986, when Johnson was getting into his eighties, he willed the house and its surrounding 47-acre campus to the National Trust, though he retained the right to live there until his death.

Small numbers
Fears that large hordes of tourists would not only overwhelm the Glass House - which is surprisingly small - but also perturb the locals has made this a site you have to put on your calendar.

Only small groups will be allowed in, and access is by advance reservation. Before he built the Glass House, Johnson saw plans for Mies van der Rohe's glass-walled Farnsworth House near Plano, Illinois.

Johnson borrowed the idea, refined it and finished his own glass house before Mies could finish his. Although both are now under National Trust stewardship and both are icons of modernism in America, they seem conceived in a very different spirit.

Mies raised his house off the ground, which makes it seem something like an altar for priestly living - a sacred space apart from nature. Johnson's glass house is simpler and more rooted in its landscape.

Johnson's house is also rooted to its dark twin, the Brick House, which sits across a small patch of grass. They were built at the same time, as a single, unified structure with two very different faces.

Two kinds
Everything that cannot be done in the Glass House can be done in cosy seclusion of the Brick House, the main bedroom of which is entirely covered in cloth panels.

Seen as a single entity, the Glass House and Brick House add up to a mind-blowing unity. And at the level of its mechanical systems, the two-house dyad seems like a metaphor for the brilliant man.