Me and a friend have a half-baked (in more ways than one) idea that it would be fun to move to Detroit and get into aquaculture. It's something we managed to romanticize. Give it some steam-punk marketing aesthetic for giggles.
(I think half the value of HN is being able to browse your old comments to remember where you saw something very interesting.)
Wow, I've been thinking about this a lot. I thought I was the only one :)
Although I was kind of thinking a bit larger - building a whole new city within a city - completely self sustaining. With 100M it might be possible :)