One of the adventures of the fellowship in The Lord of the Rings, chapter 8. The Barrow-downs are flat topped hills converted to burial grounds by the ancient race of Men, who called it Tyn Gorthad. While passing through the Barrow-downs on their way from the Shire to Rivendell, the party is captured by Barrow-wights, who perform a mock burial of Merry, Pippin, Frodo, and Sam in the style the burials of the ancient Men. Tom Bombadil comes along and saves them.
There's a song the Barrow-wights sing.
Cold be the hand and heart and bone,
And cold be sleep under stone:
Never more to wake on stony bed,
Never, till the Sun fails and the Moon is dead.
In the black wind the stars shall die,
and still on gold here let them lie,
till the dark lord lifts his hand
over dead sea and withered land.
The reference to The Dark Lord isn't out of place. The Barrow-wights were originally sent to the Barrow-downs by The Witch King, later to be leader of the Nazgûl, from his kingdom of Angmar. So these guys are basically working for Sauron.
For etmology see: barrow, down, wight. source: The Encyclopdia of Arda, http://glyphweb.com/arda