A wooded hollow is called a dell. A dell is usually a small, secluded valley that is usually in a forest.

A small, secluded, and often wooded valley is known as a dell or in Scotland as a glen. A wide, flat valley through which a river runs is known in Scotland as a strath. (from https://en.wikipedia.org/wiki/Valley)

That is the correct spelling of "secluded" (out of the way, remote).

Secluded means far from society. It can also means obscured from sight, such as "in the secluded woods."