Dead Marshes

The Dead Marshes is a fictional place from J. R. R. Tolkien's universe, Middle-earth.
Literature.
Once a part of the ancient battlefield of Dagorlad, the Dead Marshes lie north-west of the Morannon, the principal entrance to Mordor. The Battle of Dagorlad was fought there, at the end of the Second Age, when the Last Alliance met the forces of Mordor with many casualties on both sides amongst Elves, Men, and Orcs. Through the years, the marshland began to encroach upon parts of the battlefield, and engulfed the dead that lay there.
The Marshes are also known as 'The Mere of Dead Faces'; they are described in The Passage of the Marshes in "The Two Towers" as "dreary and wearisome. Cold, clammy winter still held sway in this forsaken country. The only green was the scum of livid weed on the dark greasy milky surfaces of the sullen waters. Dead grasses and rotting reeds loomed up in the mists like ragged shadows of long forgotten summers." 
On their way to Mordor to destroy the One Ring, Frodo Baggins and Samwise Gamgee are led through the marshes by Gollum. They see the aforementioned dead, Gollum stating, "Only shapes to see, perhaps, not to touch." Frodo is mesmerized by the candle-like lights that appear to float over the Marshes (called by Gollum "candles of corpses"); those who are hypnotised by these lights, and who therefore try to touch the bodies, are likely to drown in the waters and join the dead. In the book, Gollum reveals the dangers to Sam, who calls to the stiff and lifeless Frodo and breaks his trance before he can touch the waters.
Not far away is another dismal swamp, the Nindalf or Wetwang, beside the Emyn Muil hills.
Inspiration.
In a 1960 letter Tolkien said that "the Dead Marshes and the approaches to the Morannon owe something to Northern France after the Battle of the Somme."
The medievalists Stuart D. Lee and Elizabeth Solopova compare Tolkien's account of the Dead Marshes to the monster Grendel's wilderness in the Old English poem "Beowulf". 
Portrayal in adaptations.
Peter Jackson's flying Nazgûl background shots were filmed above the Kepler Mire, a massive string bog between the towns of Manapouri and Te Anau in the Southland Region of New Zealand. It can be viewed on the Mt York Road some 2 km east of the Highway 95 turn off.
The close-up shots were filmed on the Weta Digital Wet-Set at Lower Hutt, NZ.