We enter a high place or tall building (5)
I believe the answer is:
tower
'tall building' is the definition.
(I've seen this before)
'we enter a high place' is the wordplay.
'enter' means one lot of letters goes inside another.
'a high place' becomes 'tor' (I've seen this in another clue).
'we' inserted inside 'tor' is 'TOWER'.
'or' acts as a link.
(Other definitions for tower that I've seen before include "Steeple" , "Stand tall" , "tractor, perhaps" , "Reach high" , "Drawer" .)