From A Wiki of Ice and Fire
George R. R. Martin has not published the location of Raventree on maps yet, but the non-canon map for HBO's Game of Thrones places Raventree north of Riverrun and the Red Fork and south of the Whispering Wood. The Lands of Ice and Fire indicates the castle is north of Riverrun, west of Fairmarket, and southwest of Oldstones.
The castle has high, ancient stone walls with moss climbing up them. There are two huge, square towers flanking the gate and a square tower at each angle in the wall. It is also defended by a deep moat lined with stone. Inside the walls there is a muddy outer ward, a cavernous timber keep and a godswood. Lord Blackwood's solar is large and airy, with great beams of dark oak. Wool tapestries adorn its walls, while latticework doors with panes of diamond-shaped yellow glass overlook the godswood.
Raventree's godswood contains a dead, ancient weirwood of colossal size. Every evening at dusk hundreds of ravens come and roost all night on the dead weirwood as they have for thousands of years. It is claimed to have been poisoned by the Brackens.
A Game of Thrones
A Storm of Swords
A Feast for Crows
A Dance with Dragons
In the wake of the Red Wedding and the following submission of Riverrun and Seagard, Raventree Hall is the last castle in the Riverlands refusing to declare for King Tommen Baratheon. Jaime Lannister goes to Raventree and negotiates the surrender of Lord Tytos, taking his son Hoster as a hostage to ensure Tytos's good behavior. Tytos intends to have the bones of Lucas Blackwood, another son who was killed at the Red Wedding, buried beneath Raventree's great weirwood.