From the back of the box:
Descend deep into the interior of the earth, as you lead the three curious and heroic adventurers from Jules Verne's classic novel: Professor Lidenbrock, his nephew Axel, and their guide Hans. Begin your amazing journey by dropping into the crater of the dormant Icelandic volcano Snaefells. Explore a dense forest of giant mushrooms, traverse a turbulent underground ocean, and then get hurled out of an Italian volcano to return to the earth's surface.

On your epic journey discover fossils both small and large, collect gold, and overcome dangerous obstacles. Explore the many parts of the vast subterranean cavern, using clever orienteering, critical equipment, and luck to overcome each new challenge along your breathtaking path. The player who escapes with the best collection of natural treasures wins! Will you direct our heroes on a journey of danger, discovery, and fortune?

From the rules:
The players slip into the roles of three courageous explorers: mineralogy professor Otto Lidenbrock, his nephew Axel and their Icelandic guide Hans Bjelke. You explore the inside of the earth in three stages. You descend down the dormant Icelandic volcano Snaefells. You then cross a turbulent underground sea. Finally, you escape through a volcanic eruption on the Italian island of Stromboli. You make important discoveries by cleverly using equipment like Ruhmkorff's famed induction (electric) lamp, in search of fossils and experiences that will bring you international acclaim. By earning the most fame points you win!

Game Summary
The board has 3 areas: the descent through the mountain, the journey across the lake, and the exit through the volcano (~5 min only). There are 3 explorer tokens (red, yellow, blue) and 2 types of cards: equipment and explorer (players start with equal number, same mix of cards; there are face up cards and face down draw decks). Explorer cards are used to move explorers (3 colors; 1 card = 1 movement pt for that color explorer) while equipment cards modify movement.

In the first 2 parts, on your turn you either take 3 cards (any combination of face up/down explorer/equipment cards) OR move orthogonally; if moving, must advance (1 level deeper in mountain, 1 column further across in lake) at least 1 row/column. Each space costs 1 MP; some cost more (shown as 2 or 3 rocks). Equipment allows you to move diagonally, or get across pits/whirlpools, or make rock-spaces only cost 1 MP, or give you bonus MP. Moving over some spaces gives you a water token. If you end on specific spaces, you may discard a combination of 1-3 equipment cards (pictured on board) to draw as many fossil cards (lamp allows you to draw an extra fossil card to choose from). At the end of the Mountain part, you may keep 3 fossil cards for every water you discard. In the lake phase, all explorers are on 1 raft, so any single color may be used to move the entire raft.

After moving and resolving lake space effects, draw a random event card (may hurt someone or give bonus VP if [un]able to discard specific combo of explorer cards). The player getting the first explorer to the end of the Mountain, or the raft to the end of the Lake, scores bonus 4 VP. In the final Volcano phase, draw random explorer card and move raft to next like-colored space; players must discard cards shown, or pay penalty.

At the end, score VP = sum of values of fossils (various types, sets score higher if you have more parts of the set) + bonus VP + 1 VP/water token. Most VP wins!

Humboldt's Great Voyage