Create a garden inside a mountain if you're so inclined.
As well, it allows you to lay topsoil over smooth stone. Researching 'Farming' opens up the ability to plow soil, which lets you further increase the fertility of rich soil. You can also create raw compost and turn it into fertilizer, which can be used to upgrade your soil, even turning regular soil into rich soil.
Without researching anything, 'Fertile Fields' allows you to do basic terrain modification, essentially just digging up dirt from one spot and moving it to another. New Research and Terrain Improvement Options:
