The official definition for what defines the item in this collection is: "Huge mass of structured metal or concrete, not a train or a car". So it's cranes, abandoned buildings, pipelines - anything made by engineers that's cool. This collection is still under construction, there is a lot of stuff in my favs that belongs here (that's why I made it in the first place) but that I didn't get around to putting in yet. Don't let that discourage you from looking around, of course. Note to self: Done until page 23