We have some invisible hills around here, but the ones I'm thinking of aren't invisible at all. They're visible enough that the foundations of the houses are obviously built up on one side to keep it level, and the rooftops are nowhere near even. I'm thinking that maybe the info on routeslip isn't reliable, or I used the csgnetwork incorrectly.

OTOH, we definitely have some of those "invisible" hills, too. The nice thing is that one of the main ones is on the way to the cafe where we often eat breakfast, which means coming home from eating, it's downhill. (wink)