But Portmeirion is much more than just a fancy film location. It is the embodiment of one man's belief that it should be possible to build on a very beautiful site without spoiling it, and that with sufficient sympathy and skill one can even enhance nature's beauty.

Portmeirion has been variously labelled as "pastiche", "light opera", "romantic", "exotic". In truth it is all of these and more - a giant landscape painting in three dimensions that the viewer observes and enters. It was created by visionary Welsh architect Sir Clough Williams-Ellis as a serious piece of architectural propaganda.

Shortly before he died in 1978, Williams-Ellis wrote "Amid humanity's general hubbub one small squeak has been mine - pleading the cause of beauty." This was the driving force behind everything he did: as a founder of the Council for the Protection of Rural England; in over sixty years as an architect; as a town planner; and in his extensive writings.

After writing and speaking at length on the pleasure of architecture, on landscape design and the preservation of the countryside, it was inevitable, that he should one day practise what he preached. He also hoped to bring appreciation of architecture and design to an audience who might otherwise be put off by the technicalities. He set out to prove that "architectural good manners can mean good business".

Although Williams-Ellis was in his early forties when he began Portmeirion, the desire to create a group of buildings to his own design had been with him since childhood. He had toyed with the idea of an island location and visited over twenty islands. How else, he reasoned, could he protect it from other development? But he came to realise that inaccessibility would work against him as well - he could never hope to cover the cost of shipping the necessary equipment and materials.

After travelling half way round the world in search of a suitable site, he discovered the perfect location almost in his own back yard.

In 1925 an uncle asked if Williams-Ellis knew of anyone who might care to buy a coastal property, then named Aber Ia. Though it was less than five miles from his home, Williams-Ellis had only ever seen the place from the sea. Its tenant, an eccentric recluse, had refused entry to everyone. When he visited the peninsula and saw its "beetling cliffs and craggy pinnacles, level plateaux and little valleys, a tumbling cascade, splendid old trees and exotic flowering shrubs", Williams-Ellis realised that he had found his ideal site.

He bought it and immediately began planning his development. Work began modestly with the renovation of existing buildings, starting with the old mansion house on the sea's edge. A gardener's bothy was reconstructed as Mermaid cottage. A stable block was converted to become The Salutation. Two new cottages, Angel and Neptune, were added before it tentatively opened in 1926 as a hotel.

Williams-Ellis used the first few years to establish key highlights, "pegging-out" the boundaries of the village as he put it. He created landmarks such as the "Watch-house" perched precariously on the edge of the cliff; the "Campanile" giving the place its distinctive skyline and signalling to the world that something was happening; and the "Chantry" way up at its highest point. Thereafter he would fill the gaps between with less important structures choosing styles and colours to compliment, or contrast with, these "focal points" as scene and mood dictated.

There is no single architectural style. Gothic arches frame Palladian façades. Steep pitched Italian roofs nestle alongside Georgian houses. And the emphasis throughout is as much on the frivolities as on the structures themselves. Arches and gateways, belvederes and balconies, fountains and statues - gaiety and whimsy are everywhere and everything.

Williams-Ellis was brilliant at framing views. Ready composed snapshots offer themselves at every turn. He was also a master of false perspective, playing tricks with scale, making arches too low, and statues too small, creating the illusion of height and distance. The Unicorn, with its pink portico front, is a perfect illustration - looking exactly like a replica Chatsworth House, closer inspection reveals it to be just a two-roomed bungalow.

The Campanile is made up of stone remnants from a 12th century castle that had stood nearby, crowned with a concrete structure using forced perspective to exaggerate the height. The upper windows are really half the size one expects.

Describing his bell tower Williams-Ellis wrote, "I had just picked up a splendid and melodious old chiming turret clock from a demolished London brewery." It was one of many such acquisitions. As a seamstress might collect fragments of fabric for later use, so Williams-Ellis collected bits of buildings - a fireplace here, a set of iron railings there - hoping he would find use for them later. He invariably did, and to great effect.

Not built until 1959 the "Pantheon" feels as though it should have been there from the start. To millions of Prisoner fans it was "The Green Dome", home of the mercurial "Number Two". Built for its contribution to the skyline, which Williams-Ellis perceived to be suffering "severe dome-deficiency", the original dome was plywood painted green to look like weathered copper. In 1992 it was finally roofed in real copper.

By the early seventies Portmeirion was almost complete and Sir Clough, then in his late eighties, felt able take more of a back seat: as he put it "no longer a dictator, more a counsellor and critic." If popularity was a measure of success then his experiment in sympathetic development had succeeded beyond even his expectations. He had set out to generate interest in architecture, planning, landscaping and design in an uninformed public. Portmeirion was drawing thousands of visitors from all over the world: individuals and families; organised parties; photographic and horticultural societies; students; even groups sponsored by the British Council. It also attracted great interest from both the English and Welsh Tourist Boards.

Williams-Ellis's remaining concern was how to preserve Portmeirion after he had gone. But, by the time of his death in 1978 his creation was protected, its future assured by a series of astute moves. From the early island-hopping days Sir Clough was determined to safeguard Portmeirion from external development. After buying the old house, the site of the village and the tongue of land beyond, he had gone on to acquire more and more hinterland, neighbouring Deudrath Castle, its park and avenue, the Gwyllt headland gardens and the adjoining farms, creating an exclusion zone around the property. Fears of future meddling were addressed in 1973 when Portmeirion was given Grade II listed building status. The Department of the Environment scheduled the place as of "Architectural and Historic Importance".

Portmeirion became so well protected that an architectural journal reported at the time that it took Wiliams-Ellis nine months to obtain the necessary listed building consent to add a window to one building - the authorities arguing that it was not in keeping with the architect's original intentions!

In 1993 Portmeirion's future was further secured when it was designated a Conservation area, ensuring it would continue to bring joy and a "touch of the Mediterranean" to its many fans for years to come.