Robotnik's headquarters was the main base of operations for Dr. Ivo Robotnik in Robotropolis. Formerly Castle Acorn, after the despotic mad scientist's coup the castle along with the rest of Mobotropolis was technoformed into a polluted wasteland. After Operation: EndGame the House of Acorn retook the castle back and stated to change it back to it's old carnation before Robotnik's coup. Unfortuanitly Mobotropolis was retaken by Dr. Eggman, though the HQ was destroyed along with the rest of the city by nukes from Station Square.