Bench-cum-library-steps, at Coughton Court, Warwickshire (inv. no. 135342). ©NTPL/Andreas von Einsiedel
In response to the previous post Margaret McAvoy asked how that bench at Coughton Court actually transforms into a set of library steps.
Regency-period 'Patent Metamorphic Library Chair' by Morgan and Saunders (inv. no. 871315) in the Library at Saltram, Devon. ©NTPL/John Hammond
So here you can see how it works: you simply flip it on its side and ascend the little steps inserted between the legs.
The armchair 'metamorphed' into a set of steps. ©NTPL/John Hammond
I have found a few more images of ‘convertible’ library steps.
Chair that converts into steps, in the Library at Penrhyn Castle, Gwynedd, built 1820-1832 by Thomas Hopper for George Hay Dawkins-Pennant. ©NTPL/John Hammond
There seems to be a variety of ways to transform chairs and benches into steps, and it clearly appealed to the cabinetmaker’s ingenuity.
Bench containing a set of library steps, supplied by Thomas Chippendale in 1767-8 for the Library at Nostell Priory, West Yorkshire (inv. no. 959724). ©NTPL/Jonathan Gibson
There are some relatively simple and modest examples, and complicated and grand ones by the likes of Chippendale.
The Nostell Priory library steps unfolded. ©NTPL/Andreas von Einsiedel
You can do some more browsing for library steps in the National Trust Collections database.