By Jemima Laing
The collection consists of 29 undated volumes
More than 150,000 historic books from 160 National Trust properties have been catalogued online for the first time.
And among them is a collection of miniature children's books from A La Ronde in Devon.
The collection consists of a wooden box whose sliding lid is painted to resemble a bookcase.
But quite how the books - 29 undated volumes, mostly from one series, all of about 1700 - ended up at the 16-sided property near Exmouth is not certain.
The unusual property was built for two spinster cousins, Jane and Mary Parminter, on their return from a grand tour of Europe in the late 18th century.
It contains many objects and mementoes of their travels.
The interior decoration includes a feather frieze, gathered from native game birds and chickens, laboriously stuck down with isinglass, and a fragile shell-encrusted gallery, said to contain nearly 25,000 shells.
"But the books date from before Jane and Mary's time," said Sarah Jane Kenyon, house steward of the National Trust property.
"So it's not quite clear how they got here."
The sliding lid has been painted to resemble a bookcase
The 29-strong set is made up of miniature school text books and the smallest is Westminster Abbey Vol 2 by Thomas Boreman - which measures 5cm x 6cm.
The largest is Mrs Norton Storybook: composed for the amusement of her children, which is 7.5cm x 12 cm.
"You can read the books, depending on your eyesight, you might need a magnifying glass," said Sarah Jane - who recently joined the team at A La Ronde.
And she jumped at the chance to clean the miniature books - which are cleaned periodically.
"I said 'I'm doing those'!
"You do it using a pony hair brush to brush off the dust. And then opening the pages very carefully you check a few pages for pests.
"You just have to be really careful."
But there is still the puzzle how the miniature books ended up at A La Ronde - there are other examples in the Bodleian Library and at London's V&A.
The Parminters were childless spinsters and it is difficult to see why they might have wanted children's books.
But the National Trust's website says the answer may have come to light by accident.
During a public lecture in London in 2001, the Trust's Libraries Curator was told by a member of the audience who grew up in Exeter in the 1930s that he had a clear memory of a set of miniatures being on sale in a shop in the city.
So it may be that the set was acquired for A La Ronde at that time, perhaps to boost the tourist appeal of a house already packed with curiosities.
And Sarah Jane agrees about the collection's appeal.
"They are definitely worth seeing, they are extremely cute."