"I did actually find a 'secret passage' in my grandmother's garden - she lived in an old monastery for a period! There was a tunnel which lead to a local chapel."
Gosh, this sounds like Five on Finniston Farm
! You should have kept going! You don't know what you might have found!
I absolutely love secret passages/tunnels! The more the better, I say! For this reason, two of my all-time favourites are:
The Island of Adventure
- this has just about everything you could want: - a secret passage from the sea caves into the cellars under the children's house; an underground copper mine on the island; a well shaft on the mainland AND an undersea tunnel connecting the well to the mine! Fantastic!
The Secret of Spiggy Holes
- this is also a double-whammy with a tunnel from the sea caves to the children's boarding house, and another secret passage inside the building's walls to the old house nearby.
I could go on but I know other people will no doubt have their favourites that they may wish to contribute.
I would add that Enid Blyton's ability to clearly describe events occurring in closed spaces (eg tunnels, passages etc), often in darkness, was one of her (many) great abilities as a writer. The children may be in the dark but the reader always has a wonderful awareness of what's happening.