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)

Fans dressed as Darth Vader and Chewbacca take a boat trip to the Skelligs on May 4, 2018 in Portmagee, Ireland. The first ever Star Wars festival is taking place against the backdrop of the famous Skellig Michael island which was used extensively in Episode VII and Episode VIII of the popular science fiction saga. The small fishing village of Portmagee, which is closest to the location, has seen a boom in tourism following the latest films. The vilage will host a Star Wars drive-in and a Star Wars themed Irish dancing competition over the weekend. (Photo by Charles McQuillan/Getty Images)

“Cheddar Gorge is a limestone gorge in the Mendip Hills, near the village of Cheddar in Somerset, England. The gorge is the site of the Cheddar show caves, where Britain's oldest complete human skeleton, Cheddar Man, estimated to be 9,000 years old, was found in 1903. Older remains from the Upper Late Palaeolithic era (12,000–13,000 years ago) have been found. The caves, produced by the activity of an underground river, contain stalactites and stalagmites”. – Wikipedia

Photo: A general view of Cheddar Gorge is seen on March 22, 2012 in Cheddar, England. With only a few months to go until the opening ceremony of the London 2012 Olympic games, Britain's tourist industry is hoping to benefit from the influx of athletes, officials and visitors. (Photo by Matt Cardy/Getty Images)

“The Red River Hog (Potamochoerus porcus), also known as the Bush Pig (but not to be confused with P. larvatus, common name “Bushpig”), is a wild member of the pig family living in Africa, with most of its distribution in the Guinean and Congolian forests. It is rarely seen away from rainforests, and generally prefers areas near rivers or swamps.

Red River Hogs eat grass, berries, roots, insects, molluscs, small vertebrates and carrion. They are capable of causing damage to plantations. Red River Hogs typically live in herds of 6-20 members led by a dominant boar. Sows rear 3-6 piglets at a time.”

Photo: Two 17 day old red river hoglet twins forage for food next to their mother Bahiti at London Zoo on August 23, 2007 in London, England. Red River hoglets inhabit the forests and swamps of West and Central Africa. The recent additions to the London Zoo pig pen have been eagerly awaited by zoo keepers. (Photo by Chris Jackson/Getty Images)

Back dropped by planet Earth the International Space Station (ISS) is seen from NASA space shuttle Endeavour after the station and shuttle began their post-undocking relative separation May 29, 2011 in space. After 20 years, 25 missions and more than 115 million miles in space, NASA space shuttle Endeavour is on the last leg of its final flight to the International Space Station before being retired and donated to the California Science Center in Los Angeles. Capt. Mark E. Kelly, U.S. Rep. Gabrielle Giffords' (D-AZ) husband, has lead mission STS-134 as it delivered the Express Logistics Carrier-3 (ELC-3) and the Alpha Magnetic Spectrometer (AMS-2) to the International Space Station. (Photo by NASA via Getty Images)

Construction continues on One World Trade Center (TALLEST BUILDING AT LOWER LEFT) as the memorial footprints of the twin towers are seen (BOTTOM C) on August 12, 2011 in New York City. Upon completion, One World Trade Center will be New York's tallest skyscraper, topping out at a symbolic 1,776 feet, with 3 million square feet of office space. More than 2,700 people were killed when al-Qaeda terrorists hijacked U.S. passenger jets and flew them into the twin towers of the World Trade Center on September 11, 2001. Nearly ten years after the crippling attacks on Lower Manhattan, business, tourism and new construction like One World Trade Center have rejuvenated the formerly devastated cityscape.(Photo by Mario Tama/Getty Images)

Deputies of the opposition fight with deputies of the majority for a second time in two days, during the second session of the newly elected Ukrainian parliament in Kiev on December 13, 2012. (Photo by Sergei Supinsky/AFP Photo)

A Mongolian Shamaness or Buu, beats her drum while taking part with others in a fire ritual meant to summon spirits to mark the period of the Summer Solstice in the grasslands on June 22, 2018 outside Ulaanbaatar, Mongolia. Banned for 70 years under Communist rule, shamanism has seen a resurgence in Mongolia since 1992, when the ancient practice became protected by the country's Constitution. Known as Tengrism, in which Shamans channel ancestral spirits, it is widely regarded as Mongolia's national religion and part of its indigenous identity. (Photo by Kevin Frayer/Getty Images)