Our historic towns are a precious cultural treasure. I've been exploring them for decades, extracting secrets about the ways people built, lived, toiled and took their pleasures through the generations.
A particular joy is the great diversity in the building materials and methods with which towns were built. Within a few miles the very nature of the settlements can change, depending on available materials. So you find brick in much of south-east England, timber in Herefordshire and Worcestershire, limestone in Somerset and the Cotswolds, sandstone in Cumberland, and granite in much of Cornwall and Scotland. Architectural and building styles also change, evolve and survive in a most charming way, to give each town its own vernacular character.
The most beautiful and best- preserved of our historic towns are well-known, and rightly so, but one of the wonders of these islands is that many fascinating places are taken for granted or overlooked. Ludlow in Shropshire is a perfect example: rising on a plateau above the river Teme on the border of England and Wales, it was a frontier town and fortified with wall, gates and a mighty castle.
It was also a market town, so it has a long wide market square and a "shambles" of alleys once home to victuallers and butchers. But best of all is its glorious mix of building materials and styles. You find 16th- and early-17th-century timber-framed structures with late Gothic or Renaissance details – such as the Feathers Inn – jostling with sedate brick-built Georgian houses. A stroll through the city gate and up Broad Street – lined with the mansions of long-forgotten rural grandees – is a great urban experience.
Frome, in Somerset, is very different. It is primarily a limestone town, its houses built of square ashlar blocks or coursed rubble rendered with lime. Its golden age was in the 17th and 18th centuries, when it flourished as a market and coaching town and a centre for the wool industry. The old weavers' quarter, called the Trinity, dates from the late 17th century and incorporates charming and pioneering industrial housing. It was almost swept away in the 1970s but, at the 11th hour, enough was saved to remind us of what had been, and give extra character to this most rewarding town.
As with all the best towns, the pleasure of a walk through Frome is far more than the sum of its parts. The spaces, the sustained streets, the sinuous forms, the vistas framed and enclosed, the surprise as corners are turned and amazing buildings or compositions emerge, offer great aesthetic thrills. There is Cheap Street – lined with early buildings, steep, paved and with a central gutter or "canal", once a common feature in our towns and cities – the steep and cobbled Catherine Hill, Stony Street and Gentle Street with their generous Georgian houses, and the astonishing temple-like early 18th-century Rook Street Chapel.
For urban brick at its best, explore Blandford Forum in Dorset. Here the town centre, destroyed by fire in 1731, was soon rebuilt in a splendid English baroque manner by equally splendidly named local builders the Bastard brothers. The bricks are of superb quality and colour, and the way they are laid and detailed displays superlative craftsmanship and deep sensibility. Add to this the Bastards' eye for baroque styling, particularly fashionable in the West Country: facades articulated with pilasters and dressed with details inspired by the work of Borromini in Rome.
It's all amazing, and organised around a splendid baroque parish church, also designed by the Bastards. This heady combination of grand church and swaggering houses gives this little town the architectural sophistication and, at moments, the presence of a great city.
For yet greater 18th-century architectural and metropolitan sophistication in a smallish town, visit Stamford in Lincolnshire. Here all is stone-built – to the highest quality – and baroque in spirit. The building types – theatre, assembly room and elegant shops as well as large terraced houses – act as reminders that provincial towns were once the centres of their own world, places of culture, sophistication, fashion and local pride.
A walk through the streets of Stamford today offers striking contrasts. There is wonderful 18th-century architecture – the memorable George Hotel on St Martin's offers a vivid vignette of the glorious age of coach travel – and there are the more commercial streets, now too often strewn with litter and lined with bland shopfronts and chain stores.
In Wales the coastal town of Tenby, with its nearly complete late-13th-century walls, was created as a fortified redoubt of English and Flemish settlers and merchants within Wales. Much survives of this period, but there is also evidence of the town's brief time as a resort for the early-19th-century novelty of therapeutic sea-bathing. So elegant walks look onto splendid beaches that were once part of the town's medieval defences and by the Regency period were picturesque attributes of a fashionable pleasure.
Among defensible towns, little can compete with Berwick-upon-Tweed, the long-disputed border town between Scotland and England. It has Britain's only complete set of 16th-century town defences, and within these the town is mostly Georgian, including a sprawling early-18th-century barracks designed in bold and masculine baroque manner by Sir John Vanbrugh's Office of Works.
One of my favourite towns, and one often overlooked, is Armagh in Northern Ireland. Its two cathedrals, both dedicated to St Patrick – one medieval and Protestant, the other mid-19th-century and Catholic – eye each other from high ground at either end of Armagh. Because of the cathedrals and its administrative importance, Armagh was made a city in 1994, one of the UK's smallest. Both cathedrals are remarkable – the Protestant one largely because of its glorious monuments, the Catholic one because of its astonishingly ornate and colourful Gothic Revival architecture.
But for me the great glory of Armagh is its domestic and civic architecture, much of it Georgian and the legacy of an enlightened late-18th-century Protestant cleric, Archbishop Richard Robinson. He gave the town a number of buildings of fine design that express admirable and civilised virtues, including a handsome neo-classical public library, built in 1771, and an observatory, built in 1790.
More visually thrilling are the streets: the park-like Mall, lined on one side with splendid late-Georgian houses, and, best of all, the terrace on Vicars Hill, by the Protestant cathedral. The house facades have no ostentatious detail: the doors are simply marked with blocks of stone, the windows no more than holes punched in the rendered wall. But what holes! In their proportions and relationships they reflect classical design stretching back to the Renaissance, Rome and beyond. In their humility and self-effacing beauty, they are emblematic of all that is best about UK architecture.
• Dan Cruickshank presents BBC2's The Country House Revealed, and Brick by Brick: Rebuilding Our Past
