A stone's throw from John O'Groats - which is not quite the northernmost point of mainland Britain but still feels like the edge of the world - this classic mediaeval structure has had only six owners since it was built in the late 15th century. In recent years it has been restored and renovated into a supremely luxurious getaway destination, with suites in the castle and a range of self-catering cottages in the surrounding 1200-hectare estate, including a "treehouse" nested in a 150-year old sycamore. There's also a fishing bothy on a private loch, and an in-house Highland pub called The Smuggler's Inn.
Rooms from $380 in low season, ackergilltower.com.
The so-called "mists of time" seem to be especially thick in the Scottish Highlands, as no one is entirely sure how far this castle dates back - it might be more than 900 years old, or as young as 500. Either way, it's a long-established part of local history. The former seat of the Davidson clan, it was used as a hospital for allied soldiers evacuated from Dunkirk in 1940, and is now a relatively affordable premium hotel, with 20 en suite bedrooms overlooking Cromarty Firth and the Black Isle, and ready access to the golf courses and mountain ranges of the Cairngorms National Park.
Rooms from $115 in low season, bespokehotels.com/tullochcastlehotel.
CASTLE OF PARK
Castle of Park is a warm pink colour, rising like a blush from the green cheek of rural Aberdeenshire. I once spent a couple of days in this cosy and intimate 16th-century Z-plan stone fortalice (there are only three bedrooms, one of which is in the castle library). The owners have reversed the general trend toward modernisation, and refitted the interior with antique furnishings and paintings. I remember taking some great walks around the wooded grounds, and tearing through a couple of novels by the fireplace, while pleasantly tipsy on quality whisky from the nearby Balvenie distillery.
Rooms from $190 a night, castleofpark.co.uk.
Built relatively recently - that is, the early 19th century - Stobo is technically more of a manor house in a "castellated style", with a roster of previous owners that includes a baron, a countess, and a wealthy English cricket player. Since the mid-1970s, the castle has gradually established itself as Scotland's only dedicated spa resort, offering an ever-expanding range of advanced health and beauty treatments. I hear it's great in summer - if and when the sun comes out in the Scottish borders - but my own visit was over Christmas, when the hotel offers a pretty magic package of festive feeding and pampering.
Treatment packages from $225 a person a night (based on two sharing), stobocastle.co.uk.
The former family home of the Mackenzie clan, Kincraig began life as a late-period sandstone castle before being softened and reclad as a white-harled Scottish baronial house early in the 20th century. It now stands as one of the more quiet and romantic accommodation options around Inverness - a short drive from that city but entirely secluded within its own private grounds. The "castle" rooms offer four-poster beds and spectacular views across the firth, and the in-house restaurant is one of the best in the region. The complimentary dram of Dalmore single malt whisky on check-in is a welcome touch, too.
From $400 a person for dinner, bed and breakfast, kincraig-castle-hotel.co.uk.
There are in fact two Inverlochy castles just outside the Highland town of Fort William - one is now a picturesque ruin, the other a former baronial mansion just two miles away. The latter was built 700 years after the original, but was given an early and ringing endorsement by Queen Victoria, who stayed for a week in 1873 and claimed that she had never seen "a lovelier or more romantic spot". The modern hotel has 17 rooms, each with its own distinct traditional design, but also tricked out with 21st-century "essentials" - DVD players, laptops, and PlayStations on request.
From $450 a person for dinner, bed and breakfast, inverlochycastlehotel.com.
The writer was a guest of Castle of Park.