falling through terrain

Ok, so I am currently trying to make a simple map with a few buildings on it. While adding buildings in, I tried to enter the game and I fell through the terrain. I never did anything to the controller or terrain. Any ideas of what when wrong?

 

Are you saying you didn't fall through the terrain before having added buildings? I don't see how the buildings would change that.
If you disable/remove the buildings does the issue fix itself, and you don't fall through?

 

After I added the buildings I started falling through and even if i delete them I still fall through. I feal like I clicked the wrong button or something.

 

As methos5k already asked, did you test it before adding buildings? If so, did it work?

You could have made changes (initially or after adding buildings) that could have affected this, like altering Physics settings and setting your player (layer) not to collide with terrain (layer), or simply remove/disable some of the colliders, etc. etc.

Just save current Scene, start a new one and attempt rebuilding basic elements (player and terrain) there to see how it works. If it does, you can check what's different in the main scene. If it doesn't, well, you might be making a mistake in the basics...

 

This happened to me the first time I worked with terrains. Everything was fine until I added some hills. Then I kept falling through. I figured out that somehow the terrain was now at 100.0z instead of 0z even though it said in inspector that it was at 0.0z. I simply moved my player to 100.98z and everything was fine again. Is this maybe what happened to you?