My nephew decided he wanted to dig a hole to China a little while ago, which I thought was harmless enough and a good thing to keep him out from underfoot without putting him in front of the TV.
Unfortunately, I didn't realize how very tenacious he was.
He just kept digging pretty much all day, and eventually he came and told me that he had found something and when I went out to see, it was a pipe! Luckily he came and told me rather than trying to break it or something.
I don't know what the pipe was for, but at that moment I decided it was time to explain to him how very big the earth actually was.
So I guess I have my own little "pipe locator" if I ever need one.