When engineers design heat-pump-based geothermal heating systems for homes and other buildings, they can use coil loops buried around the perimeter of the structure to gather low-grade heat from the earth. As an alternative approach, they can drill well casings and store the summer's heat deep in the earth, then bring it back in the winter to warm the buildings. To understand how heat can be stored in the earth and how it propagates through soil, this article presents four interesting experiments that teachers and their students can carry out using a relatively simple apparatus consisting of a wooden box, some inexpensive accessories, and various types of soil. (Contains 3 figures.)