Concrete steps. It's a simple thing, and so common as to be unremarkable. Exactly the sort of detail on wants to create a realistic scene. Crisply molded, it would be a simple matter to cut a step or two off the bottom for a shorter flight. The only reason I dropped it to 4 stars is the color is nearly pure white. A darker grey would help, as would some speckles (if done to scale). Nothing that can't be fixed by a coat of paint and a bit of weathering though.