I am looking for a word or an expression (or a way to describe) all spaces that are not outdoor or in open air, such as:
Basically anything with walls :).
Options I considered:
- indoor -- suitable mostly for man-made spaces and it doesn't go well with natural tunnels or caves.
- confined spaces -- it is too restrictive; I want to convey the idea of a space you can explore.
Is there such a word or expression ?