City of Steam, although one particular landmark looms above the rest. It's the Colossus, a slumbering defensive... thing that rests in the city proper, and Mechanist Games has an amusing post giving a bit of backstory to the machine.
Apparently the Colossus was created a long time ago as a giant mobile fortress tasked with protecting the city in times of dire peril. As the city is more or less at peace, the Colossus is in stand-by mode -- although it could be woken at any moment.
This mega-sized robot features cannons and an arm that's good for punchin' and aught else. The devs revealed that originally it had several more limbs, but revisions turned it into a walking fort instead.