The many hills of San Francisco feature some of the most desirable, and expensive, homes to be found anywhere. But unless these homes are on the tops of those hills, they don't often have level land beneath them. The Bay Area, and a good bit of the rest of California, is also very earthquake-prone.
It would seem unwise to build a house on stilts in this place, but people do.
I'm sure they do it very well... but still. This example sits on the side of Forest Hill. I think it has about 3 feet of frontage that's attached to the actual hill. The rest juts out over a VERY steep slope. The views are magnificent, but I wonder if the residents ever give our geology a thought.