A moratorium is in effect on adding information from Fire and Blood until December 20th.
Whitewalls, nicknamed the Milkhouse, was the second castle of House Butterwell. Its location on maps has not yet been published, but it was located in the riverlands. The castle was built near the Gods Eye, with the Butterwell lands on the eastern shore of the lake. Whitewalls was closer to Maidenpool than to King's Landing.
Costly to build, the pale castle was commonly called the Milkhouse by those who lived near it. Its walls, keep, and towers were made of white stone quarried in the Vale of Arryn, and its floors and pillars were crafted from white marble veined with gold. The rafters were carved from the trunks of weirwoods. The castle had a great hall, a sept, a gatehouse, yards, a kennel, kitchens, a cellar, and a well.
Whitewalls was built forty years before the Second Blackfyre Rebellion, about 171 AC, by Lord Butterwell, who had been Hand of the King to Aegon IV Targaryen. Some seventy to eighty years before the War of the Five Kings, one could take a ferry across the Trident from the crossroads inn to the road that led to Lord Harroway's Town and Whitewalls. However, the river moved and the ferry landing at the crossroads inn was abandoned.
The castle was the site of the wedding tourney at Whitewalls in 211 AC. While journeying from Stoney Sept to the kingsroad, Ser Duncan the Tall and Prince Aegon Targaryen took Ned's ferry across the Gods Eye to attend the festivities. The Second Blackfyre Rebellion failed at the tourney, and Lord Ambrose Butterwell forfeited Whitewalls to the Iron Throne. Lord Brynden Rivers, Hand of the King to Aerys I Targaryen, ordered the castle pulled apart and its earth salted.
I mean to pull it down stone by stone and sow the ground that it stands upon with salt. In twenty years, no one will remember it existed. Old fools and young malcontents still make pilgrimages to the Redgrass Field to plant flowers on the spot where Daemon Blackfyre fell. I will not suffer Whitewalls to become another monument to the Black Dragon.