Remember how as kids we thought that if we could dig a whole deep enough, we'd end up in China? (I seem to remember a recent commercial about that) Well, the truth is, we'd end up in the Indian Ocean! A really cool Google Maps mashup allows you to drag a map that will show you where a point on the opposite side of the Earth is.
Wouldn't this be a fun activity for students learning about latitude and longitude? Do you think they could come up with the formula for how this works?