Mirkwood

Mirkwood was the name of the Maeotian marshes which separated the Goths from the Huns in the Norse Hervarar saga. It also appears in other works from Norse mythology, such as the Lokasenna. The Old Norse word myrkviðr means "darkwood"; mirk is Old English for "dark", cf. murky. The name was borrowed by J. R. R. Tolkien as the name of a great wood east of the Misty Mountains in Rhovanion, in his fictional Middle-earth.

Tolkien's Mirkwood
Mirkwood was the forest dwelling of a Silvan Elven kingdom, ruled by King Thranduil. It had been called Greenwood the Great until around the year 1050 in the Second Age of the Years of the Sun, when a shadow of the dark lord Sauron fell upon it, and men began to call it Mirkwood, or Taur-nu-Fuin and Taur-e-Ndaedelos in the Sindarin tongue. Sauron established himself at the hill-fortress of Dol Guldur on Amon Lanc, and drove Thranduil and his people ever northward, so that by the end of the Third Age they were a diminished and wary people, who had entrenched themselves beyond the Mountains of Mirkwood (Emyn Fuin, formerly the Emyn Duir or "Dark Mountains"). The Old Forest Road or Old Dwarf Road crossed the forest east to west, but due to its relative proximity to Dol Guldur, the road was mostly unusable. The Elves made a path farther to the north, which ended somewhere in the marshes south of the Long Lake of Esgaroth.

In The Hobbit, Bilbo Baggins, along with Thorin Oakenshield and his band of Dwarves, ventured into Mirkwood during their quest to regain Erebor from the Dragon Smaug. There, they came across many great spiders, the breed of Shelob. Shortly after the Dwarves' escape, they were captured by the Elves. After or during these events the White Council attacked Dol Guldur, and Sauron fled to Mordor, and his influence in Mirkwood diminished for a while.

Years later, Gollum, after his release from Mordor, was captured by Aragorn and brought a prisoner to Thranduil's halls. He escaped during an Orc raid, and fled south to Moria.

After Sauron was reduced to a powerless "spirit of malice" at the conclusion of the Third Age, the darkness was lifted from Mirkwood, and it became known again by its old name of Eryn Lasgalen, Sindarin for the Wood of Greenleaves.