The Underground Boat is a sailing route that travels across an underground sea between two holes in the Earth's crust at Reykjavik and Snowdon. It flies the flags of both America and Denmark.

The underground boat is only accessible after meeting explorer Otto Lidenbrock in Reykjavik and hearing how he has successfully found evidence of a world beneath the surface of the Earth. Upon hearing of the various exit points Otto has discover, Mr. Fogg jumps at Snowdon, realising its proximity to London could help secure his wager.

The underground boat is exceptionally fast, owing to calm oceans and there being nothing in the way to slow it down.

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