Landscape remains in a box upside-down (5)
I believe the answer is:
vista
'landscape' is the definition.
(I've seen this in another clue)
'remains in a box upside-down' is the wordplay.
'remains' becomes 'si' (I am not sure about this - if you are sure you should believe this answer much more).
'in' indicates putting letters inside.
'box' becomes 'tv'.
'upside down' says the letters should be written backwards.
'a'+'tv'='atv'
'si' going into 'atv' is 'atsiv'.
'atsiv' backwards is 'VISTA'.
Can you help me to learn more?
(Other definitions for vista that I've seen before include "Prospect, view" , "Panorama" , "Panoramic scene" , "View (with avenue)" , "Perspective" .)