Castle MacNeil is a castle in Scotland appearing in the Archie Comics continuity. It was the home of April O'Neil's Scottish ancestors, the MacNeils - particularly one Sandy MacNeil, chief of the clan during the late 1600s.
Sandy held darkness in his heart, so when the woman who loved him, Elan, gifted him the Sword of Destiny, it amplified his evil and encouraged him to conquer. Elan and her sisters attempted to steal the sword back. Sandy woke up and stabbed Elan with a dirk, but she secured the sword long enough to flee with it and hide at the very top of the highest tower of the castle, where she died of her injury. Her sisters were left to rot in the castle's dungeon when they refused to give up her whereabouts. The women's spirits all became banshees, haunting the castle ever since.
Centuries later, April Splinter, and the Turtles would come to visit April's uncle Tam MacNeil, caretaker of the castle. Due April to meeting Elan and having visions, Tam becomes convinced that they must find and retrieve the sword. As the group scales into the castle, Tam is held hostage by Shredder, who was spying on them with Krang and was told by the latter that the sword was a powerful alien weapon. Splinter, the Turtles, and the banshees fight off Foot Soldiers, and the banshees also help April stave off Krang as well. April eventually climbs to the top of the tower, where she finds Elan's bones and the sword. Realizing how much power the sword has and what it could do in the wrong hands, she casts it into the Loch Ness. Splinter also knocks the two villains out of a window and into the lake. Doomsday Hassle in Banshee Castle