This location is the headquarters of Anti-Cosmo, and acts as his evil lair. It is here where the Anti-Fairies gather to discuss their plans for world domination. Anti-Wanda also gave birth to Foop here in the episode, "Anti-Poof". The sign over the castle's entrance says "Anti-Cosmo's Castle Welcome. Not!"
The castle is colored black and dark blue, with sharp spiked towers and a purplish colored Rainbow Bridge covered with spines. The castle is usually seen surrounded by dark or red ominous clouds.