Henry and his Uncle, Professor Hardwigg, lived in a manor in Germany. They lived in a comfortable mansion, studying in the lab and reading in the library. Unfortunately, the reader is not told much more about this location, so I cannot give it any more information.
Mount Sneffels is the mountain where Henry and his Uncle enter the earth. It is a cold, harsh, portion of Iceland, an extinct volcano. It took Henry a long, hard climb to reach the summit, and then enter the deep cavern, where they descended via ropes and hooks.
At the bottom of the crater, there are two galleries, one of which leads to a dead end, and one of which leads to the Central Sea. Made out of solid rock, these tunnels in the earth go “downhill” if it’s an acceptable expression for a place where there aren’t really hills.
The Central Sea is a large ocean spanning many leagues. The roof in this great cavern is also high enough for clouds to form, and a luminescent material glows across the ceiling, allowing for fairly good vision when on the sea. Storms and the like also form here, much like on the surface.
Near the sea, all sorts of ancient life forms said to be extinct inhabit the land, including a man-like creature as large as fantasy giants, and woolly mammoths. The Ape Gigas, predecessor to the African Gorilla, also made an attack on Henry’s party. Henry did not explore much in this area, as his Uncle was anxious to be on his way deeper; however, when they attempted to blow up a passage, a volcanic eruption occurred, sending them flying upwards through a volcanic shaft, where they were spat out on the side of a tropical volcano. They were then able to travel back home to Germany.