There's a local pub that has stone effect inside, which is basically cladding a wall with polystyrene rock shapes. (it's probably not actually constructed from PS as it has a bad fire safety rating, so you might want to check that out). It's very convincing and you'd only notice if you actually felt it as it's not as cold as stone would be. You know the "stunt rocks" you see on TV; ones that look real but then some pipsqueak picks it up and flings it no bother - that's the kind of thing.
Rebecca