US workers visiting old railway workshop (10)
I believe the answer is:
laboratory
'workshop' is the definition.
(scientific workshop)
'us workers visiting old railway' is the wordplay.
'us workers' becomes 'labor' (US spelling of 'labour').
'visiting' becomes 'at'.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'railway' becomes 'ry' (abbreviation for railway).
'labor'+'at'+'o'+'ry'='LABORATORY'
(Other definitions for laboratory that I've seen before include "Where researchers work" , "Place for experimentation" , "Experimental facility" , "Experimental area" , "Place of scientific research" .)