Here one may spend time underground (7)
I believe the answer is:
dungeon
'time underground' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'here one may spend' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'one' is 'eon' which is within the answer.
The remaining letters 'dung' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for dungeon that I've seen before include "old prison" , "Dark underground cell for prisoners" , "prison the result" , "Keep" , "Place of confinement underground" .)