Classicly

At the Earth's Core by Edgar Rice Burroughs appeared in serial format in 1914, the first in a series about the "hollow earth" world of Pellucidar. Burroughs, the "Prince of Pulp", never had much of a handle on scientific accuracy, but he never let it get in his way. This is the tale of friends David Innes and Abner Perry who use a massive drill to plow in the the core of the earth. There they find a land of strange humanoids, wild beasts, reptilian creatures and some enslaved humans.

The only light available is from the radioactivity of the rock, which has somehow frozen time. Innes and Perry must face outlandish perils unknown to survive… and to win the heart of the beautiful leading lady. The book is super entertaining old school sci-fi. It might be more enjoyable for the teenage set, since some of it seems comically inaccurate and out of date. But as with most Burroughs, you're guaranteed a fun, fast paced read. The Pellucidar series is another set of the author's work which is sure to please sci-fi fans, old and young alike.