Talk:Key Items/@comment-36048757-20180724012058/@comment-33896168-20180802224832

that's part of Cerberus's request. after accepting the request, talk to the minotaur in the Grand Noah blacksmith shop I believe. She tells you all the minotaurs were invited to a party. near the end of the tunnel south of the castle in your pic, there should be a minotaur that gives you an invitation that should let you in.

also, said tunnel minotaur wants you to bring her 10 dishes of sukiyaki, which are a drop from the minotaurs in the castle. I'm pretty sure the reward was a medal that lets you recruit the boss of the castle.