From A Wiki of Ice and Fire
and the approximate location of Greywater Watch
Greywater Watch, also known as Greywater, is the seat of House Reed in the North. It is roughly located in the swamps of the Neck, southwest of Moat Cailin. It is a castle built upon a crannog, one of the man-made floating islands of the swamps, and it does not stay in the same place, making it impossible for ravens or enemies to find. According to Meera Reed, there is no maester there, nor any knights or masters-at-arms.
Ironborn and Andal warriors, including Freys, have attempted to conquer Greywater, but none have been able to find it. Many of the invaders rode into bogs and sank because of their armor.
A Game of Thrones
Robb Stark sends word to Lord Howland Reed at Greywater to have the crannogmen defend the Neck if Lord Tywin Lannister marches up the causeway.
A Clash of Kings
Meera and Jojen Reed travel from Greywater to Winterfell to meet Bran Stark.
||"Their houses move, even the castles like Greywater Watch." 
- Little Walder Frey
, to Theon
References and Notes
- ↑ 1.0 1.1 A Clash of Kings, Chapter 21, Bran.
- ↑ 2.0 2.1 A Clash of Kings, Chapter 50, Theon, p 733.
- ↑ "Greywater Watch" entry in A World of Ice and Fire
- ↑ A Clash of Kings, Chapter 28, Bran.
- ↑ A Storm of Swords, Chapter 24, Bran.
- ↑ A Game of Thrones, Chapter 55, Catelyn.