|Universe||The Elder Scrolls|
"Looking up slightly at the massive root structure above, Scotti saw something wriggle past. An eight-foot-long, armless, legless, colorless, boneless, eyeless, nearly shapeless creature, riding the roots."
Rootworms are a species of eyeless, boneless worms indigenous to the swamps of Black Marsh, on the continent of Tamriel which lived their lives riding along the roots of the trees in the area. At an adult size, they are massive; thanks to a thin skin as well as breathing holes dotting their bodies, travelers could make use of them to enter a rootworms' stomach and ride along inside of them in a method referred to as the Underground Express. Though this process is likely very messy by its very nature, it could be considered a better choice than braving the dangerous local wildlife, including the fleshflies and hackwings.
Surprisingly, despite that one could ride inside of one of these creatures, they were only approximately eight feet long. A colorless species, the Rootworms migrate in the winter from northern regions of Black Marsh and towns such as Hixinoag to southern regions and cities such as Gideon. They are extremely fast and can cover the distance between these two locations in a matter of several minutes.