A "gravity hill" is a slope that appears to be sloped the other way, and a "false flat" is a slope that appears to be flat. One example that most people don't realize is the Munich gravel plain (
https://en.wikipedia.org/wiki/Munich_gravel_plain) - even though it has the word "plain" in its name, it actually has a very slight gradient going up toward the mountains to the south, because it's formed from gravel eroded from the Alps. Once you are aware of it, you do notice that it takes a little bit less effort to cycle northward rather than southward, and you can also see it if you look at your car's current fuel consumption.