Another instance of imprisonment in what sounds like an “oubliette.” Rather famous one, this - James Hepburn, 4th Earl Bothwell. I recalled reading something about his imprisonment in a book, and looking for a link to cite came upon this account of a relatively recent visitor to Dragsholm Castle in Denmark, where Bothwell was imprisoned for some ten years prior to his death.
If use of the oubliette as a dungeon is folklore, it goes back quite a way, it seems. From the autobiography of Benvenuto Cellini (1500–1571):
spoke- - Regarding the concealed doors for servants, they are relatively common in mansions/manor houses. They are frequently panelled/painted the same as the rest of the wall, but have a shallow handle set into them, to be unobtrusive.
Doors like this are often used elsewhere in manor houses - “secret” private entrances to libraries via small spiral staircases leading to a concealed door of that nature (often painted as another bookcase, or indeed having the false backs of very truncated books and bookshelves on it) are relatively common & I’ve seen several myself in the UK, but can’t recall the name of where offhand, I’m afraid. Trompe l’oeil effects went through a popular phase too, with some actual doors being painted to resemble paintings, or three dimensional objects (I’ve seen a very good one that appears as though a violin is hung on the door) probably about the same time as the false doors.
Of course, this is a later time period to the secret passages of the OP.
I’ve never heard tell of oubliettes at english castles being used for food storage when I’ve visited them. I also thought I had seen at least one in an entranceway which actually dropped people back outside the castle again - either in the moat, or onto the ground/midden. That may be a faulty memory though, I’m afraid.
Regarding secret passages, I have a friend who built one into his house. It’s cool. There is a large 3-section bookshelf built into a wall, and one of the sections swings backward, books and all, to reveal another room (where he kept his networking equipment and servers, of course). I’ve always wanted to have one of those.