Structures missing during game play.

I did something and now my walls and floors disappear when I play the game. Any ideas what I did to cause this? How to fix this?

 

FPS Minigame tutorial. They are there, just not visible. It only affects the main Scene, not the Secondary scene. I think I deleted something off the Hierarchy.

 

You're probably going to have to show screenshots or video explaining what you're talking about. The issue is, the knowledgeable people on the forum haven't done a beginner level tutorial in many years, and none of the people who are currently doing beginner tutorials will have the confidence to answer support questions. So ask your question in a way which assumes no prior knowledge of the specific tutorial.

As far as how things can disappear, there's a large number of possibilities. The GameObjects could have been destroyed (you'd see them disappear in the scene Hierarchy), the renderer components could be disabled (they would be unchecked in the Inspector if you click on the specific GameObject), they could be on a render layer which the Camera is set to not display (you'd look at the layer setting on the GameObject and compare that to the layers the Camera is set to show), the GameObject could be too far from the Camera putting it outside the Camera's far clipping plane, the Camera could just be facing the wrong direction, etc, etc, etc, many more possibilities.