Workplace where skates are useless (6)
I believe the answer is:
office
This might be a double definition.
'workplace' is the first definition.
(I've seen this before)
'where skates are useless' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
(Other definitions for office that I've seen before include "Where a white-collar worker works" , "Administrative unit" , "Position, or building in which colours in layers" , "Department" , "Business premises" .)