On the western side of Mount Hood lies the longest glacier cave system in the contiguous United States. In 2012, these caves were mapped to a combined length of 7,166.8 feet by cave explorers Brent McGregor and Eddy Cartaya. Currently, the total passage length is hundreds of feet less. Glaciers are frozen rivers; they are always moving and changing... (Photo and caption by Josh Hydeman)

A photographer has captured these eerie images showing the scale of some of Britain's deepest darkest wonders. Mike Deere, from Reading, heads to daunting locations such as abandoned mine shafts, miles of sewer tunnels that snake underneath London and even disused cooling towers. Photo: This incredible picture was taken at the Box Freestone Mine, in Wiltshire. Mike revealed that even experienced map readers would struggle to navigate their way around the seemingly endless tunnels that he and his friends visit. (Photo by Mike Deere/Caters News)

Dharma the Sumatran tiger yawns as members of the public return to Edinburgh Zoo as it opens for the first time following the easing of Scottish Governments lockdown restrictions on June 29, 2020 in Edinburgh, Scotland. Outdoor visitor attractions in Scotland have reopened along with many non-essential retailers after more than three months in lockdown, as Scotland moves into phase 2 of its “route map” for easing coronavirus restrictions. (Photo by Jeff J. Mitchell/Getty Images)

Indian Runner ducks march past farm buildings at the Vergenoegd wine estate near Cape Town, South Africa, May 16, 2016. Each day, a quack squad of killer ducks are released for the first of two sorties at South Africa's Vergenoegd wine farm in Stellenbosch. Their mission – seek and destroy thousands of pests out to ruin the season's harvest. Fanning out across the vineyards, some 1,000 Indian Runner ducks hone in on their hidden targets with uncanny precision, locating the tiny white dune snails feasting on budding vines. (Photo by Mike Hutchings/Reuters)

Isabella Santiago of Venezuela (C) is kissed by runner-ups after she was crowned Miss International Queen 2014 at the transgender/transsexual beauty pageant in Pattaya November 7, 2014. Some 22 contestants from 18 countries, all born male, competed in the week-long event for the crown of Miss International Queen. (Photo by Athit Perawongmetha/Reuters)

Costumed competitors run during the Marathon International du Beaujolais race near in the gardens at the castle of Pizay, November 22, 2014. Its 10th edition gathered more than 10,000 runners from 60 countries making their way on small roads, around and through the castles and vineyards, in the Beaujolais region. (Photo by Robert Pratta/Reuters)

A runner tries to get the attention of a bull, named Santon, during the “Toro de Cuerda” (Bull on Rope) festival at Plaza de Espana square in Grazalema, southern Spain, July 18, 2016. Three bulls restrained by a rope are allowed to run through the streets of the village during the annual festival. (Photo by Jon Nazca/Reuters)

Runners high-five children cheering from the sidewalk as they begin the half marathon during the Ottawa Race Weekend, which returned from a two-year hiatus due to the COVID-19 pandemic in Ottawa, Canada on Sunday, May 29, 2022. (Photo by Canadian Press/Rex Features/Shutterstock)