Natural walls and floors

Walls and floors resembling the bark and inner wood of various trees, heavy vine curtains, dirt/clays, etc.

Imagine wondering a lush forest, brushing through a thick curtain of low hanging vines, revealing a massive tree with a door built into it. Through the door is small humble dwelling. Who lives here? Perhaps the old hermet you've heard tell of, or one of the shy reclusive druids who only visit town for eccentials once or twice a year.