This is a weird graphical glitch that I found down in the Jury Street Tunnels of Fallout 3. The static models inserted by the level designer flicker in and out of view depending which way you face. The actual model data and collision box is still there, but the model becomes invisible.

I'm not sure whether this is because of a mod that I've added, a hardware issue, or whether it was a bug in the base game. I suspect it's a mod issue, but I haven't tracked down which one. (It's also a location that I tend to only visit once, so I don't care too much.)