Get inspired to put unexpected enterprises in unusual places. This inspiration came from hearing a radio program about farming fish on land.Human ingenuity can find solutions in so many unexpected ways.
An entrepreneur in NSW (Australia) noticed, when he took his family fishing to his childhood fishing haunts, that the fish just weren't biting anymore. This inspired him to first develop a sustainable terrestrial fish farm himself, then grow it into a business designing, building and exporting them.
The aquaculture is complemented by hydroponic vegetables and the fish suffer various fates - mainly as table fish in city restaurants but other products too.
Maybe fish farming isn't the answer for your space - but another innovative (perhaps off-beat) enterprise can be.