From A Wiki of Ice and Fire
The Crag is the seat of House Westerling. The Crag is more of a ruin than a stronghold as House Westerling no longer has the funds to maintain it. It sits along the coast. Rolph Spicer was the former castellan of the Crag before his betrayal of House Westerling and Robb Stark.
A Clash of Kings
A Storm of Swords
The Crag was stormed, with Smalljon Umber and Black Walder Frey scaling the walls, while Robb Stark broke through the main gate. Robb Stark took a wound and was nursed back to health by Jeyne Westerling. During the nursing, Robb deflowered Jeyne, and being an honorable man, married her shortly thereafter. As a consequence of that, the Westerlings joined with House Stark.