Even a small box can grow a surprising amount of veg. My bf set up a box of about 1 x 3 m, 60cm high, filled it with manure, branches, straw and other organic matter, and planted butternut squash, sweet potatoes, chili, sunflowers. It looked mad when it reached its prime, like some c movie garden tentacle monster. So far we got 25 butternut squash, endless chili, and we have eaten the first few sweet potatoes. It's on top of stone slabs, not even soil. Or a community garden, or guerilla gardening. Many things involving plants or animals are very rewarding and make one more happy.