I think the author wrote this book to let us know that nothing is
impossible.  This book is about three people who tried to do the
impossible.  They were Prof. Hardwig, his nephew Harry, and their guide
Hans.  They were on a journey to the center of the earth.  They were
trying to follow the path of Arne Saknussemm, a brilliant professor and
chemist of the sixteenth century.  Harry and his uncle found a parchment
written by Prof. Saknussemm describing a trip to the center of the earth
down through a volcano.
The trio was going down the volcano named Mt. Sneffles.  On their
journey, they encountered, mastodons and animals like plesiosaurs.  They
also saw a caveman that was at least twelve feet tall.  His head was the
sign of a buffalo's.  They also encountered a terrible storm.  During
their adventure they learned you shouldn't start something unless you
Know what you're getting yourself into.
If you like action-packed books where you never what will happen on the
next page, you'll love this book.  The author makes it easy to see in
your mind what is happening.  I really enjoyed this book because I like
action-packed books.  If you're about ten years old and you need a
little more action in your life, this is the book for you.