A map showing the location of Goldengrove on the continent of Westeros.
Goldengrove is a castle in the Reach, it is the seat of House Rowan. The castle is located north of Highgarden near the border of the Westerlands.[1]
In the books
In the A Song of Ice and Fire novels, Goldengrove is the seat of House Rowan. In the novels, Lord Mathis Rowan is one of Lord Mace Tyrell's closest and most trusted advisors (along with Paxter Redwyne and Randyll Tarly) and has a reputation for steadfast prudence that is known even outside the Reach. He accompanies King Renly Baratheon on his campaign. Notably, in the novels it is to him that Catelyn Stark makes the remark about Renly's followers being the 'knights of summer', rather than Renly himself as in the TV series.
In the novels it was Mathis Rowan who sent Dareon to the Wall after finding him abed with one of his daughters.
See also
Goldengrove on A Wiki of Ice and Fire (spoilers from the books)
References
Template:The Reach