Castle Ravenloft is Strahd's home, a legendary dwelling that is full of unique dangers. The waffle crew explored it on multiple occasions. While Paultin was a "guest" in the keep, he saw the upper levels and the prison. When the waffle crew invaded it, they extensively searched the catacombs and ultimately defeated Strahd there.
Strahd sent a black carriage and invited the waffle crew and Mordenkainen to Castle Ravenloft. When they arrived, Rahadin demanded the Tome of Strahd. The group killed him. Mordenkainen split from the group to go destroy the Heart of Sorrow, a magical device that made Strahd more powerful.
The group went down into the crypts searching for the sunsword. They found the crypt of St. Markovia. Markovia appeared before Evelyn and blessed Lightfall. Strahd antagonized the group with an illusion.