I had the thought earlier that, if I could render texture mapped cubes in 3D, why not make a 3D tile map? And so I did using tile graphics from Blocky Man as texture maps. It's not much, but it's a start, and perhaps it can lead to a simple game of some sort.
One thing I'm still having trouble with is working the camera. As long as it just rotates about the Y-axis, and moves forward and backwards, it's fine. However, when I try to look up or down and move forward, I encounter some rather interesting problems. I'm still learning the math behind it, and I'm sure I'll get the hang of it soon enough.