Deepest, Hottest Part of the Earth, Not Outer
Puzzle 15 of Under the Ground Easy Pack
Question is: Deepest, Hottest Part of the Earth, Not Outer
and the answer is: INNERCORE
Word Meaning:
INNER CORE — (planetology) The solid material found in the centre of some planets at extremely high temperature and pressure, distinct from the liquid outer core.
Definitions from Wiktionary.