It is not the center of the earth, just underground, but they are reptiloid.
It is the best tale of underground earth dwellers I have read. though admittedly I haven't read many
Result
Hart-Davis, Adam. Deepest Mine. BBC and Open University, 2002. "The deepest mine in this region (Witwatersrand) is currently Western Deep mine, a network of tunnels which penetrates 3.5 km into the Earth's crust." 3500 m
Structure of the Earth. Geography Exchange, 7 March 2003. "The deepest mine in the world is only 3.3 km deep, and nobody has ever been able to drill down further than 15 km." 3300 m
How deep is the deepest mine? Grid Club, 2003. "The deepest mine is a gold mine in South Africa; in 1977 the Western Deep Levels reached a depth of 3,581 meters. 3581 m
Lotsberg, Gunnar. Mines. The Worlds Longest Tunnel Page, 2003. "It has the world's deepest mine, 3585 m below surface at the East Rand mine." 3585 m
Holt, Rinehart, & Winston. Environmental Science. 1996: pg 210 - Figure 8.17. "This open-pit copper mine in Bingham, Utah is wider than 35 football fields and more than twice as deep as the Empire State Building." 896 m