Most pet cats will become timid or defensive when outdoors, but not Millie – after being adopted by her mountain-climbing owner Craig Armstrong, Millie has become a feline hiking and mountain-climbing legend.

Audrey Lu and Misha Mitrofanov of the United States compete in the Pairs Short Program during day 1 of the ISU Grand Prix of Figure Skating Rostelecom Cup at Megasport Arena on November 15, 2019 in Moscow, Russia. (Photo by Maxim Shemetov/Reuters)

Emma Coburn (L) and Colleen Quigley of the U.S. look at the scoreboard after competing in the women's 3,000 metres steeplechase final during the 15th IAAF World Championships at the National Stadium in Beijing, China August 26, 2015. (Photo by David Gray/Reuters)

Japan's Kana Muramoto and Chris Reed compete in the figure skating team event ice dance short dance during the Pyeongchang 2018 Winter Olympic Games at the Gangneung Ice Arena in Gangneung on February 11, 2018. (Photo by John Sibley/Reuters)

Women practice swimming with mermaid tails at AquaMermaid swimming school, a mermaid training school in Chicago, United States on March 19, 2017. Participants are fulfilling their lifelong ambitions of becoming mermaids with a new type of fitness mermaid swimming. (Photo by Bilgin S. Amaz/Anadolu Agency/Getty Images)

Three-month old cheetah cubs make their public debut at the Smithsonian National Zoo on July 24, 2012 in Washington, DC. (Photo by T.J. Kirkpatrick)

Masked participants stand in St.Mark's Square during the Carnival on February 10, 2007 in Venice, Italy. (Photo by Marco Di Lauro). P.S. All pictures are presented in high resolution.

A Shi'ite worshiper bleeds after cutting his scalp in a ritual display of mourning during an Ashura commemoration ceremony outside Kadhimiya shrine on December 6, 2011 in Baghdad, Iraq. Ashura marks the death of Prophet Muhammad's grandson the revered Imam Hussein in Karbala, Iraq in 680 AD. Shi'ite festivals were prohibited during the time of Sunni dictator Saddam Hussein's rule. (Photo by Mario Tama/Getty Images)