The biggest 'crack' I've ever had in one of my games happened in Monte Vista. That's a store world. I wanted to build a 5 story house into the side of a hill. I found a hill and placed a new lot using the tool in Edit Town then made a large flat area into the side of it. I started working on my build when the whole side of the hill gaped open and I could see underneath the other terrain as if it was a huge basement. I couldn't fix it so I started a fresh save.
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