From A Wiki of Ice and Fire
and the location of Torrhen's Square
Torrhen's Square is a castle in the North and the seat of House Tallhart. It is located southwest of Winterfell, near a large lake. It has stone walls 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 comes under attack from ironborn. Ser Rodrik Cassel takes the better part of the Winterfell garrison to respond to the threat. Once there, he breaks Dagmer's shield wall in the Battle of Torrhen's Square and sends the ironborn retreating back to the Stony Shore.
A Storm of Swords
Maester Aemon sends a raven to Torrhen's Square in a plea for help to defend Castle Black from wildlings.
Dagmer returns to capture the castle, as the Tallhart forces were largely destroyed in the Sack of Winterfell.
A Dance with Dragons
Dagmer holds captive the surviving Tallharts at Torrhen's Square.
References and Notes