Winterfell is the ancestral castle and seat of power of House Stark and is considered to be the capital of the North. It is located in the center of the northernmost province of the Seven Kingdoms, on the kingsroad that runs from Storm's End to the Wall. It is situated at the eastern edge of the wolfswood, north of the western branch of the White Knife and Castle Cerwyn. Winterfell is south of the northern mountains and southwest of Long Lake, one hundred leagues (three hundred miles) southeast of Deepwood Motte.
During the Winter War the armies of Stannis Baratheon, the Umbers, and the Manderlys united beneath the walls of Winterfell, intent on reclaiming the fortress. After only three days of siege the garrison of the castle turned upon it's lord, Ramsay Bolton, and turned both him and the holdfast over to Stannis, who entered triumphantly.
That victory was not to last, however, as within the walls of Winterfell Stannis was eventually assasinated, murdered by parties unknown but largely suspected to have been Bolton men. Ramsay is blamed, and in the aftermath, burnt alive by Stannis' men.
Jon Snow would eventually return to Winterfell after the War for the Dawn, where he ruled as regent until Rickon Stark was of age.
Winterfell is a huge castle complex spanning several acres and protected by two massive walls. There is a village just outside, the winter town. Winterfell has been built around an ancient godswood and over natural hot springs. The water is piped through walls and chambers to heat them, making Winterfell more comfortable than other castles during the harsh northern winters.
Inside the walls, the complex is composed of dozens of courtyards and small open spaces. Weapons training and practice take place in those yards. The inner ward is a second, much older open space in the castle where archery practice takes place. It is located next to the broken tower. Inside Winterfell stands the inner castle, which contains the Great Keep and the Great Hall.