What could you draw?

How about a dam?

Here's a very simple gravity dam. This is actually a cross-section of the very simple gravity dam.

	The left side would be the upstream side, where the water would be. The right side is then the downstream side. The bottom edge would be connected to a foundation of rock.

Or try a gravity dam with an inspection galley (a big hole) in the middle; or try an arch dam and include some of the foundation.