Otto Lidenbrock is a character in 80 Days, a scientist and explorer looking to investigate the world beneath the Earth's crust. He is based on a character of the same name from Jules Verne's 1864 novel Journey to the Centre of the Earth.
After striking up a conversation with Passepartout in the underground city of Kristiania, Otto mentions that he is looking around the globe for entry points into the Earth's core. Passepartout recommends Iceland, famous for its volanic instability and geysers, and Otto thanks him for the suggestion. Sure enough, upon arriving in Reykjavik, Passepartout runs into Otto again - Otto was waiting for a cargo delivery aboard the same airship on which Passepartout and Fogg were travelling.
Otto reveals that he has indeed discovered a world beneath the surface of the Earth, with exit points in Kristiania, Reykjavik and, most crucially, Snowden - allowing Passepartout and Fogg to travel there at great speed aboard an underground boat.