From A Wiki of Ice and Fire
and the location of Torrhen's Square
Torrhen's Square is a castle, seat of House Tallhart and located southwest of Winterfell, near a large lake. Its stone walls are thirty feet high with square towers at each corner and a square keep. It is considered a strong keep, but not the strongest.
A Clash of Kings
Torrhen's Square came under attack from Ironborn, which led to the Sack of Torrhen’s Square. Ser Rodrik Cassel took the better part of the Winterfell garrison to respond to the threat. Once there he broke Dagmer's shield wall and sent the Ironborn retreating back to the Stony Shore.
A Storm of Swords
Maester Aemon sent a raven to Torrhen's Square in a plea for help to defend Castle Black from wildlings.
References and Notes