GERONIMO STILTON Book 4: I'M TOO FOND OF MY FUR!
Geronimo's old friend, Professor von Volt, asks him to deliver the professor's secret diary to his lab in the Himalayas. He even mentions the mythical hairy beast, the yeti, and says his life is in danger. Geronimo hates to travel but he is a good friend, so he heads out with his sister Thea, cousin Trap, and nephew Benjamin.
Their Sherpa guide, Ratfur, knows the professor is in Chomolungma --- which means Geronimo's group must climb Mouse Everest in spite of Geronimo's fear of heights. It's a long, hard climb. Just as Geronimo thinks he'll never make it, he discovers something truly astounding.