They could not be further removed from the sleek, chic glass and steel edifices of the 21st century. Ancient and crumbling, their windows are frequently tiny, staircases narrow and winding, walls awash with water, and the roof often rotted away.
Yet these "minor flaws" - in estate agents' speak - are no deterrent to the growing band of well-heeled urban professionals in love with the romantic dream of owning a Scottish castle as a place to live and work. A new breed of Highland laird - lawyers, designers and businessmen - have in recent years begun to abandon the city life to transform some of Scotland's unique collection of ruined castles into spectacular and comfortable homes.
One of the most beautiful already restored is the 16th-century Ballone Castle near Tain - where Lachlan and Annie Stewart, owners of the tartan rugs design group Anta, have lived for the past five years. But the fate of others is still in limbo - notably the 12th-century Castle Tioram at the mouth of Loch Moidart, which Winston Churchill once dubbed the second most beautiful place on earth (after the African lakes). Its owner, a wealthy businessman, has so far been refused planning permission to rescue its walls from sliding into the sea and turn part of it into a home.
Improved building technology and craftsmanship makes authentic restoration of these castles more possible than ever, while simultaneously converting them into fully equipped modern homes. "Some castles were restored in the 19th and 20th centuries, but they didn't know then, for instance, how to hide all the pipes necessary for modern living," says Stewart, who as an architect oversaw his own five-year restoration project at Ballone. "The downstairs corridors of those places consequently look like something out of a submarine. But by the time we started work in 1994, we had worked out how to conceal modern utilities to create a much better look. We have underfloor heating under the stone flag floors, for instance, so that there are no radiators on view."
But restoring Scotland's rich collection of picturesque ruins and refashioning them as modern, efficient homes with bathrooms, kitchens and ISDN lines is without doubt a daunting task. Some of these castles' walls are so thick - or are composed of the actual bedrock itself - that only a consignment of dynamite would make the necessary holes for the installation of basic utilities such as telephone or electricity.
Any restoration work is also monitored closely and must be approved by a variety of authorities from the Highlands Council to Historic Scotland - which can be both a time-consuming, expensive and deeply frustrating experience. The easiest way to gain planning permission is to avoid buying a ruin (such as Tioram) that has Scheduled Monument status, as more often than not Historic Scotland will try to block full restoration. Castles that have been considerably altered or extended within the past 200 years are unlikely to be Scheduled Monuments, so applications for permission to restore will be received, at least in theory, more favourably.
One such is the Tower of the Place of Caldwell, at Uplawmoor in East Renfrewshire within commuting distance of Glasgow. It was restored in the 18th century as a folly but is now ruined and could be bought for up to £70,000 through Beith-based agents Stewart & Osborne (01505-503345.)
Potential buyers should beware that previous applications for planning permission to restore and extend the tower have been rejected. But there are strong hopes that another sensitive plan would now be accepted. Built in the mid-15th century, it has two vaulted lower floors, an upper floor, slit windows, fireplaces and a battlemented parapet - as well as two acres of ground. It is, however, roofless and requires full restoration, but Scottish Civic Trust, which runs a website of derelict buildings in Scotland (www.buildingsatrisk.org.uk) says that frequently costs for restoring a small castle can be as little as £100,000.
"You could find yourself with a genuine Scottish castle as your home for the price of a small flat in London," says the trust's Duncan Chappell. "Although you could also spend a limitless amount of money on a project like this if you had it."
The Stewarts have found that living in a castle - even one built five centuries ago by the earls of Ross - does not preclude a fresh, modern approach to décor. Their home is quite minimalist in style. "We use all our own textiles and designed all our own furniture. We haven't used curtains as they wouldn't have done when the castle was built, but we do use them round the bed. We make sure there is no clutter on the walls and certainly haven't put up any glass-covered pictures - that would look totally wrong. It's all about being in tune but contemporary at the same time. You have to let the architecture dominate to some extent - but then that's quite fun as it forces you to think in a different way."
The popularity of Scottish castles has caused their prices to rise considerably and there is now a growing belief that there still may not be enough castles to go round. Consequently a new market has arisen for brand new castles, based on traditional designs. Stewart, a leading architect in this area, has already built two new castles from scratch, has another new one under construction in Speyside and a fourth, much bigger building at the design stage.
"These castles are still true to medieval designs - with great halls, vaulted ceilings, stone turnpike staircases and so on - but the spaces have different labels and are used for different purposes now. We even keep the traditional small windows, as most castles are one room thick so that there are windows on all sides and the inside remains light," he says.
"We have found obtaining planning permission relatively easy - even in the conservation area near Tain for example - and construction costs remain reasonable. A three-bedroom tower house castle could cost as little as £120,000 and still look like the real McCoy but with all your wires and pipes already in place and hidden away."
Lachlan Stewart architects: 01862 832 477Reuse content