Samwell Tarly mentions that Daemon II Blackfyre dreamt that a dragon hatched at Whitewalls, and perceived it as a sign that he would win the Iron Throne. However, this was just a day before the Hand of the King Brynden Rivers put down Daemon's rebellion before it even started.
In the books
Whitewalls was ruled by House Butterwell. The castle was very beautiful, made from carved white marble imported from the Vale of Arryn.
The "Second Blackfyre Rebellion", which was more of a failed plot, occurred there when Lord Ambrose Butterwell held a tournament at the castle to celebrate his marriage to a daughter of House Frey. Tourneys are often used as recruiting events for prospective knights who want to join lordly retinues in military campaigns, and the wedding tourney was indeed a clandestine excuse to gather together and recruit old Blackfyre supporters from the previous rebellion to launch a new one. The wedding was soured by the antics of Lady Frey's misbehaving younger brother - the then-three year old Walder Frey.
Brynden "Bloodraven" Rivers, the Hand of the King, said that he intended to have the entire castle pulled down as punishment for the failed rebellion.