Temperatures deep inside the earth are boiling and this heat can be used to produce electricity. Geothermal power is reliable, sustainable, and environmentally friendly – and tapping it is well worth the effort. The core of Planet Earth is seriously hot, as hot springs, geysers and volcanoes attest to. High temperatures can be found nearly everywhere at about 5,000 meters below ground. This heat can be harnessed as a source of energy. The advantages of geothermal energy are numerous: the supply is more or less inexhaustible, it can be used for heat and electricity and it barely emits any greenhouse gases. Tapping this power from the Earth\'s depths is one of the greatest technical challenges of the 21st century. GLOBAL IDEAS reporters traveled across the globe to explore the various ways in which this challenge is being met.