In context of overlay "Buildings" – Building – https://osm.org/way/1083286578 via StreetComplete 63.1:

Shed for trains, and possibly a train wash (can't see inside). Closest category in StreetComplete would be a "hanger", but perhaps there's something more railway-appropriate! 

Attached photo(s):
https://streetcomplete.app/p/346879.jpg