How do geothermal energy sources work?

Geothermal power - cold water is pumped down to hot rocks, and the steam created is used to power a turbine, to power a generator. This is only possible near volcanic areas where hot rocks are near the surface. It's reliable and it generates electricity or heat to buildings. The main drawback is that there isn't many suitable locations and the cost of building the power plant can be high. It's a renewable source.