The stairs which link different floors should be indestructible. I only paid attention to that fact once but noticed that it wasn't actually possible to damage them thoroughly. Might not apply to every type of stairs.

By the way, this is a bit off-topic, but I remember (or I looked it up to make sure, at any rate) when you asked in another thread about progression between swamp and mountains... Good job making it to the mists, feels like that happened in a flash lol.