Jules Verne wrote a novel called “Journey to the Centre of the Earth”, about an expedition starting inside a volcano in Iceland. Although the novel was fiction, scientists have been digging bore holes into the earth for decades, trying to discover what lies beneath the earth’s crust. The deepest mines only go down about 4km, but scientists in Russia drilled a research hole to over 12km deep on the Kola peninsula. After 26 years of drilling, the temperature reached 180C and the project was abandoned. Scientists have estimated that the earth has a radius of 6370km and the temperature reaches about 7000C.
Find out more at Wikipedia.