If you know the Haydon Bridge area of Northumberland then there are no prizes for recognising that Langston Castle is based upon Langley Castle a few miles south.
When I was a boy Langley Castle was a girls boarding school. On Wednesdays during the school holidays it was open for visitors to tour round and it was on one of these days that I visited with my aunt. I can't imagine the place being very comfortable then and do remember the howling gale of warm air when the turret door was open. (§ Chapter 12). Later, I had a vacation job in the castle serving as barman when the castle offered 'Medieval Banquets'.
Today Langley Castle is a luxury hotel and a favourite place to hold weddings in. It's far from the bleak castle I remember. You can visit there secure in the knowledge that Lady Triplet will not be bombarding you with smelly green water bombs.
The name means 'long open meadow' and is common in the UK. Of course this 'Langley' is nothing to do with the CIA's home in Langley, Virginia and of course the CIA is anything but 'open'.