Rather than buy a prebuilt worm farm, I took a couple discarded two gallon plant containers, lined them with scrap landscaping fabric, added some wet cardboard and topsoil, then my recently purchased earthworms. The containers fit nicely into a hole dug in the ground; I keep them covered with an old trash can lid to keep critters and sunlight away. I have steadily added kitchen scraps: coffee grounds, pulverized egg shells, vegetable peelings, etc. And the worms continue to thrive by converting the scraps into nutrient rich soil additives.
Two Gallon Worm Farm