The SEA Underground, formerly called the Satellite Transit System (STS), is an automated people mover (APM) system operating in the Seattle–Tacoma International...

terminal by a three-line automated people mover system called the SEA Underground. The underground transit system moves passengers within the four concourses...

largest is The Lost Sea, located inside Craighead Caverns in Tennessee, United States, with an area of 1.8 hectares (4.4 acres) An underground lake is any body...

SeaTac (/ˈsiːtæk/) is a city in southern King County, Washington, United States. The city is an inner-ring suburb of Seattle and part of the Seattle metropolitan...

The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts...

underground before emerging into the South China Sea The Punkva in Moravian Karst, Moravia, Czech Republic underground river flowing through cave system - Punkva...

The Underground Railroad was a network of secret routes and safe houses established in the United States during the early to mid-19th century. It was...

to six kilometres (3.7 mi) from the sea, is subject to tidal influences. Until the 2007 discovery of an underground river in Mexico's Yucatán Peninsula...

The Weather Underground was a far-left Marxist militant organization first active in 1969, founded on the Ann Arbor campus of the University of Michigan...

visits to the Irish Other World (which may be westward across the sea, underground, or simply invisible to mortals). The most famous, Oisin in Tir na...