In the latter half of the 20th century, most people commissioning a house from an architect would be surprised, to say the least, if the smallest room in the house turned out not to be in the house, but outside. And yet when Tadao Ando, a promising young architect in 1975, designed his first big commission - a town house - with the lavatory outside he got away with it.
The Azuma house, in Japan's second city, Osaka, caused a minor sensation in the architecture world. It combined ultra-modern blank concrete walls and large dollops of abstract space with little bits of history - like an interior courtyard, long abandoned by the space-conscious Japanese, and the outside lavatory, a common feature of houses before the days of public sewerage systems.
The house was built, not primarily for comfort, but to provoke. Zen masters devise their meditation puzzles for the same reason. And so started Mr Ando's career, which most recently produced Japan's wooden pavillion at the Seville Expo last year. He is bringing an exhibition of his drawings and models to London this month.
'Have you been to Ryoanji?' he asked. Ryoanji is the most renowned Zen stone garden in Kyoto: 15 stones in a sea of raked pebbles, designed by an unknown monk in 1473. 'If you feel any spiritual richness there, it is because the Japanese people have sought to live spiritually, not just physically - that is what leads to the concept of Zen.'
It was a leading question: 'The idea of a place for the spirit to live has been non-existent in Japan since the War,' he declared.
In less than 50 years, Japan has transformed itself from a devastated war wreck to the second largest economy in the world. Japanese cars and electronic goods have conquered the Earth. And yet with only a few exceptions - architecture and clothes design among them - Japan has had little of cultural value to export. Its economic progress, far from bringing a renaissance in the arts, has left a cultural vacuum behind it.
'Since the war, Japan has placed strong emphasis on the rational side, on economic development. But we have lost the spiritual richness enjoyed before the war. We must regain this, establish the irrational within the rational.' Hence the outside toilet, perhaps.
Tadao Ando is, it goes without saying, an outsider. Born in 1941 in Osaka, he never went to university, and after school became a boxer. Later he taught himself architecture, and travelled widely in Europe, the US and Africa before setting up an architect's office in Osaka in 1969. He speaks in a gruff, Osakan dialect, his hair is long, there are bags under his eyes from overwork and his clothes look permanently rumpled.
A constant critic of materialism and the gaudy display of wealth that the newly affluent Japanese are adopting, Ando likes to espouse a more austere lifestyle. This has led him to Zen. 'There are many interpretations of Zen. My view is to wander around in pursuit of something. Life is wandering in the darkness in pursuit of something.'
He described a museum he built in Kumamoto in southern Japan, on the site of ancient burial mounds. Inside the Forest of Tombs museum is a 30-metre (90ft) windowless chimney, into which visitors look straight up. 'To recreate the situation of complete darkness inside a tomb - spiritual darkness . . . that's close to the spirit of Zen.'
Ando's main preoccupation has been to get his work accepted by the conservative Japanese, who instinctively shy away from anything which threatens the established order. The uniformly boring concrete facades of the country's cities show how hard it is to create something new.
One of his greatest triumphs was the building of the Water Temple on Awaji island, off the coast of central Japan. Normally temples have multi-tiered roofs, built to symbolise the temple as a whole. Ando decided to build his temple into the side of a hill, using a lotus pond 40 metres (120 feet) in diameter as the roof. With its roots in sludge, but beautiful flowers floating on the water's surface, the lotus is an important Buddhist symbol.
'When I first proposed the lotus pond roof, everyone said I was crazy. It didn't look Japanese, what if it leaked, what if there were an earthquake and so on - the usual type of complaints. But then the head monk of the (nearby) Daitokuji temple, who was over 90 years old and highly respected, said 'I would like to see the new temple with the lotus pond before I die'. So everyone quickly fell into line and said 'let's have a lotus pond'.' Ando burst out laughing.
'I doubt if I will live to see Japan change, but I would like to see the change starting, and that is why I try to come up with new ideas.'