Architecture: Charm without the olde worlde: 'Heritage' usually equals lacklustre design. Jonathan Glancey travels to Wales to discover how it should be done

Vernacular is an ugly word, especially when its four Latin syllables translate clumsily into British architecture. What architects mean by Vernacular is a way of designing buildings in keeping with local traditions; while this sounds laudable, what they mean and what they do can be very different things.

For the most part, Vernacular is an excuse to design indifferent buildings in rural areas that pass muster with planning committees that are barmy about 'heritage' but have minimal aesthetic sensibilities. Retail giants use a pick 'n' mix Vernacular style in a vainglorious attempt to hide the coarse bulk of their ecologically unfriendly edge-of-town superstores.

Second rate (or desperate) architects use the Vernacular as a form of tweedy, jolly decent way of building: throughout Britain the same lacklustre Vernacular-style is eroding our countryside. It is the stuff of a thousand barn conversions, shops, schools and visitors' centres. It is a style set in a past present that dulls the imagination.

Which is why the three small rural buildings shown on this page come as blessed relief. In Dyfed, on the west coast of Wales, Niall Phillips, an architect based in Bristol, has shown how modest new buildings can fit snugly into the landscape without the slightest pretence of being olde worlde. These are pretty, heritage-free buildings designed to delight, built imaginatively from local materials and crafted with great care. Each has a pedagogical purpose, but none is preachy. All three enhance their beautiful settings. None is for a privileged client.

Lower Treginnis Farm, near St David's, is leased on a peppercorn rent by Farms for City Children from the National Trust. Here, 40 children at a time come to learn farming skills and to tend farmyard animals. The new building was completed four years ago. Since then, thousands of boisterous children have stayed here and, as a tribute to the skills of Niall Phillips, his project architect, Peter Roberts, and the team who built it, the farm remains in remarkably good condition.

What the architects have contributed here is a cluster of teaching rooms, playrooms and dormitories gathered around two stone-walled courtyards. At first glance, the buildings appear to be regular farm buildings. Close up, and inside, they are full of surprises and delightful architectural conceits. Designed principally for children, they offer nooks and crannies to hide away from adults, special places to sit and read and a gamut of imaginative rooms that give free play to the imagination, yet are never twee.

Here is a wonderful top-lit corridor to run down and a dining room with columns like trees. Here is a rumpus room to make a noise in; here a big inglenook fireplace and circular seats wrapped around the Douglas fir columns that hold up the deep eaves of the low-slung roofs.

Set into the stone floor of the courtyard are chequerboards for games involving pebbles and sticks. Here is a maze, and there lightshades cut into shapes drawn from Edward Lear's The Jumblies. Brass door fittings are in the guise of lizards and other creatures.

This is a place that city children with no normal access to inglenooks and stone floors find as delightful as adults for whom gentle, pragmatic, modern farm buildings are as far removed from the 'Vernacular' of superstores as Dyfed is from Dagenham. It is a tribute to the architects who spent so much time working on it - and who will never be wealthy while they continue to produce such minutely detailed, hand-made buildings.

This year saw the opening of the nearby childrens' education centre at Castell Henllys, an Iron Age hill fort at Eglwyswrw. Here is another hand- made building, sitting gently on stilts in a beautiful sylvan setting in a flood meadow facing the River Nant Duad. Castell Henllys is one of many Iron Age forts along the coast, but is particularly alluring because of its great beauty and because the Pembrokeshire Coast National Park Authority has built convincing replicas of Iron Age round houses here. As a result, it is very popular with schools. But, because it rains a lot here during term time, a childrens' reception centre was planned.

The new building can only make adult visitors to Castell Henllys green with envy. The building is very green. Approached from the path above the meadow, all it reveals to visitors is a long, curving, turf-covered roof, a lovely thing of flowers and insects in spring and summer, and excellent insulation. From the meadow, the building's elegant structure is made clear.

Constructed out of logs hewn from the surrounding forest (peeled and sandblasted to a bone-like finish), the education centre is a sophisticated kit of parts. And, yet its construction is, in part, a play on its Iron Age predecessors. The walls are made of oak boards or plaster panels limewashed yellow. The Iron Age round huts are timber structures with walls of clay and wattle. But where their roofs are thatched, the roofs of their Kevlar Age successor are of zinc and turf. The structure of the building is revealed throughout the interior and children are taught about how buildings, ancient and modern, are made with more than a little help from the shelter around them.

A pony trek away is the third and grandest of Phillips's trio of buildings, the Welsh Wildlife Centre on the Teifi marshes near Cardigan. Here visitors come to see animals and plant life. Phillips has designed the building as a big timber and glass cage for humans to stand in while Welsh rabbits (and squirrels and badgers and so on) come to peer at them.

As with the education centre at Castell Henllys, the Welsh Wildlife Centre broods gently in a hollow. Visitors come across what looks like a small cabin made of rough sawn timber boarding with a cedar shingle roof. They cross into it by a timber and steel bridge and are then surprised to find themselves on the top floor of a three-storey building complete with spacious cafe that looks out on to the fascinating landscape of the Teifi marshes.

Here, again, Phillips has designed a building rooted in the landscape that borrows from no local style, yet seems right for its remote setting. Here old and new building technologies meet in easy comradeship: rough timber construction alongside a glass wall held together with silicone joints.

In these three buildings, Phillips and his team show how a sensitive Vernacular architecture can also be progressive. It is a way of building in rural areas that needs to be explored further by British architecture. Our predecessors built in an extraordinary range of materials and styles; our best rural architecture is full of surprises. It is time to abandon the herringbone Vernacular style that threatens to turn Britain's countryside into one badly cut and mass-produced tweed jacket.

Welsh Wildlife Centre, Teifi Marshes, near Cardigan, Dyfed, 0239 621600.

Castell Henllys, Eglwyswrw, Dyfed, 023979 319.

Lower Treginnis Farm, St David's, Dyfed, 0437 720840.

(Photograph omitted)