Recent inmates like Neilson and Wisbey enjoyed relatively humane conditions. But Oxford Castle has been used as a jail since the days when the Saxons felt those Normans would never amount to anything—and, for most of its history, no tourist in their right mind would have set foot in the place. During the English Civil War, for example, 60 prisoners were crammed into each of the cells, which were then roughly the same size as my hotel room. Now, I might have been waxing whimsical about the generous dimensions of my room, but having 59 other guests to contend with would make for something of an unpleasant stay. And so it was. The prisoners were forced to lie in stacks four-deep on the floor, "easing nature" where they lay, crushed among the rotting bodies of those who died from the conditions. And no plasma-screen television, either.

Heading down for dinner at the hotel's groovy bar and brasserie, I suddenly have the alarming thought that someone may have died screaming in agony, or indeed drowning in sewage, on this very spot. Not a thought to stimulate the appetite, I can tell you. But it's actually not such a wild idea. When archaeologists recently surveyed the Oxford Castle site, they found 60 skeletons haphazardly buried in the grounds. This is perhaps not surprising, as scores have been hanged within the castle gates—although not always with the "quick drop and sudden stop" we think of. People used to be strung up to slowly asphyxiate, so family and friends would often pull on the victims' dangling legs to quicken the process….

Given this grisly past, it begs the question: Who on earth would want to stay in such a place? Well, as it turns out—plenty. Malmaison Oxford has been a glorious success. Since opening its doors in December 2005, the hotel has been lauded far and wide for its quirkiness, service and style, and boasts a full house on most nights. Somehow, this grim old space has become quite the desirable place to be.

So, how have they done it? You'd think the hotel would've tried to cover up the less-than-salubrious heritage of the building in an attempt to put their guests at ease. In fact, evidence abounds of a tongue-in-cheek celebration of the castle's penal past. The names of the various prison rooms and wings have been kept: guests sleep in A-wing, C-wing or the Houses of Correction, play pool in The Visitors' Room, and work up a sweat in The Exercise Yard.

Keeping true to the castle's history was also a priority for the designers involved in the development. "We really wanted to keep the aggression of the place, like the cell doors and the stark brick walls," says interior designer John Whiles. "But we also needed to make it a welcoming place, so guests wouldn't feel uncomfortable." To achieve this, John and his team have used soft lighting, dark colors and comforting, touchable fabrics such as velvet and wool.

The building was also made open to the public, so there is a constant trickle of tourists wandering through. One gentleman tells me he grew up in Oxford and always knew the castle as a dark, forbidding place, firmly closed to the casual gawkings of the Great British public. "It's great to be able to come inside and look around at last," he says. "What they've done is amazing." And indeed it is. The hotel is bright and stylishly appointed—everything a good hotel should be. I return to my cell room, marveling smugly at the wonders of modern development.

As I settle down to sleep, however, I start to think a bit too hard about where I am. Just what, I wonder, has been witnessed by these four walls? Misery, certainly. Death? Perhaps. In the darkness, my mind begins to race. Rumor has it that there is a "hanging cell" somewhere nearby, where executions were held until the 1950s. It's supposed to be closed to the public, but who knows? What if this is the hanging cell? I sit up and switch the light on. The room reappears, reassuringly sans noose, and I settle back onto my pillow. My surrounds are decidedly unsinister—there's nothing to worry about. Still—it wouldn't really hurt if I left a light on, would it? Just one. No one need ever know….