Atlantis Lost! — Lyle Drew

The island-continent of At-lan, having been home to the first civilization of mankind, sank as the result of a natural cataclysm, marking the end of the 3rd and final Age. The Atlanteans and their space-faring friends, the Kryloneans, escaped the destruction to wait for the rest of humankind to mature socially. Some sought the safety of the uninhabited lands to the west while a few sought alliances with the lesser races. After thousands of years, all traces of the original Atlanteans disappeared from Terra, either absorbed by other races or through relocation further away -- or were there others?
The Atlanteans dabbled in genetics research, anxious to return the years taken from their lives by their gods. Some people say that the 1st Age ended because of such research and even the end of the 2nd Age was loosely tied to their continued fascination with genetics. Now, as the 3rd Age rapidly approached, a branch of the Atlantean military escaped to Amazonia so they could continue research into unlocking the secrets of genetics. The military cut their final departure close, barely escaping when Hellene warriors located and attacked their underground base. The Hellene's decision to pursue the Atlanteans proved to be unfortunate when a malfunction trapped them in a land that no one from the surface would ever see, at least for many thousands of years.
Atlantean scouting parties on the surface heard alien sounds coming from atop an escarpment, but hundreds of years passed before they could investigate; what they discovered was a large mesa that provided an ecosystem capable of sustaining many species of long-extinct beasts. Information on the find was included on scrolls with other information deemed worthy and the lot was hidden in the base of the Sphinx. Discovered far into the future, the information on the scrolls remained undecipherable for one hundred fifty years, passed from father to son until eventually sold. The next generation produced a group of adventurers capable of understanding them -- the exploration of their secrets was on!
Their exploration headed in a direction they never anticipated when they began their search to find the grandfather of the expedition's leader, Riley Thomas. The journey began with the discovery of a long-forgotten laboratory where the team was accidentally teleported to an unearthly cavern, filled with beasts that supposedly died off millions of years earlier. Two groups of people, one savage warriors, the other technologically advanced, lived there, still living under a tenuous agreement to coexist that lasted since the destruction of Atlantis. Adopted by the technologically advanced people, the explorers learned that a subterranean route to the surface existed, but its location and the secrets of the technology that hid it were lost in history. Only Riley's grandfather might know the location of the only way back to the surface.
Adventures are many, battles are fought against man and beast, technology is discovered beyond anything known at the time, love unites the strangest of couples, the lives of dear friends are lost, and strange creatures are encountered at every turn, some of them friendly, others not quite so much, not to mention that an aging technology is failing everyone. The battle is on to find the way out before the enemy catches them or time runs out for everyone and everything in the caverns.