A building as magnificent as Thornbury Castle does not exist for five hundred years without gathering a few secrets along the way.
Many of those secrets are now locked in the past, but some are still enjoyed by those in the know, and contribute to the charm and atmosphere of this unique fortress.
Here are just a few of those secrets unlocked for your delight, so that next time you visit the Castle, your experience will feel even more special.
The Castle as we know it today was begun by Edward Stafford, 3rd Duke of Buckingham, but never finished, as he was beheaded by Henry VIII for suspected treason.
After a chequered history, the Baron of Portlethen bought Thornbury Castle in 1986 as an hotel and restaurant.
He kept a suite of rooms for himself, including one now known as the Baron's Dining Room.
He chose well; this is one of the cosiest and best-sited rooms, with windows overlooking the entrance drive to one side and the courtyard to the other.
The Baron had a playful streak, and arranged the furniture in his sitting room to the disadvantage of any hotel employee he cared to invite upstairs.
Seated opposite the Baron in the late afternoon, they would find themselves squinting into the westerly sun, while he enjoyed a clear view of the room.
The Baron also gave special instructions to his carpenter Stephen Edgar when the room was panelled in oak.
Search the panelling for a knot, press it, and a panel opens to reveal a hidey-hole containing a small safe.
Thornbury Castle's receptionists are well-used to receiving bemused phone calls from visitors who choose to stay in one particular room.
The room does of course have an en-suite bathroom, but finding it can be a challenge.
What looks like the obvious door leads to a small closet containing an ironing board. The real bathroom door is set so cleverly into the wall, and with such an unusual door handle, that it is rarely spotted.
Needless to say, that's one secret that's soon shared with the occupants.
State rooms in grand houses are designed to impress, and Thornbury Castle has its very own state bedroom, with honoured guests in mind.
You'll find "The Tower", as its name suggests, up a winding stone staircase at the top of the Castle's largest tower, with commanding views across the vineyard, the River Severn and Gloucestershire.
This is your only chance to stay in a "state bedroom" in an English hotel, and indeed your only chance to sleep in what must be the biggest hotel bed in England.
It's a massive ten feet wide by six and a half feet long, and is fitted with two sets of sheets and blankets sewn together.
As it's such a long way to the end of the bed, you'll be pleased to hear that the footboard houses a 52" plasma television that rises up at the touch of a button - just remember to take the remote control to bed with you!
The Tower was completely restored and refurbished under the guidance of English Heritage.
No expense was spared on the decoration. Two huge walls are screened in silk at over £100 a metre, and even the wooden panelling that skirts the room has been silk upholstered.
The icing on the cake though, is the gilding. You'll see it on the panelling, the doors and the chandeliers. It's 24 carat gold, and it glows.
The apple wood chandeliers in The Tower and its bathroom were rescued from a store of old furniture, carefully resanded and in places even re-carved to bring out the full relief of the design, then gilded in silver, platinum and gold.
Opposite the bed, a copy of a famous picture of Bacchus (Roman god of wine) sits in a vast Adam frame, splendidly re-gilded.
Inspiration for designing The Tower came from its original owners, the Staffords, and a sense of what they would have wanted from a state bedroom.
Like the sculptor Michaelangelo who claimed he simply removed the unwanted wood surrounding an angel in a piece of storm-damaged tree, for the restorers of The Tower it was a case of paring back previous layers of decoration, assessing the proportions and bones of the rooms, and then working to enhance them.
And when you know that your furnishings are likely to last for over two centuries (and yes, the silk can be taken down and cleaned of mucky fingerprints when necessary), it's practically an economy!
If you get the feeling you're being watched as you wander around the Castle, you may be right: there's a face in the stone embedded above the staircase that leads you to the Portlethen and Bedford rooms.
And then there's the grumpy gargoyle...
Named "Brian" after long-serving former manager Mr Jarvis, he was gilded and installed in the gatehouse.
On the south side of the Castle you'll see part of the outer wall extends in a U-shape. This is divided down the middle into two rooms.
Strangely, one room is larger than the other, and the suspicion is that there may be a priest hole in the blocked-off space.
A Victorian tunnel starts at the entrance to the former dungeon (now the wine cellar), runs under the courtyard, and comes up by the (now unused) Castle well.
It's highly likely that there was a tunnel linking Thornbury Castle and St Mary's Church, so the blocked-off triangle might lead underground.
Keep these secrets to yourself, or share them with others – it's your choice.
Just be aware that there is much more to learn – and what better excuse for a return trip to Thornbury Castle?