"Limestone walls" refers to walls that are made of or constructed using limestone, which is a type of sedimentary rock that is composed primarily of calcium carbonate. Full definition
No ski runs with sudden turns, no sheer limestone walls. (netquote.com)
The floor is made of unstable clay, and the flaky limestone walls can be easily damaged by fluctuations in temperature. (discovermagazine.com)
The rooms are decorated in traditional Maltese style with cooling limestone walls, honey - coloured wooden furniture and warming red and brown fabrics. (luxurytravelmagazine.com)