I've wanted to draw this for the last couple years. Its right next to a job site I worked on two years ago. I recently started working on a site next door, so I finally took the opportunity to draw it.
It is a huge tank of some sort. Two cannon looking things are mounted on top. They remind me of those telescope things at the beach you pay a quarter to use. The staircase winds around probably half the perimeter down to a landing.
Here are a couple other recent sketches.