As it says, you have to complete the map which means getting 100%. Here is a link to a picture of the 100% map for reference.
https://twitter.com/ConvictedofFun/status/114200882990904524...EDIT: BinaryRuse has a more complete map screenshot than I do. You'll notice two extra hidden rooms in the Underground Sorcery Lab.
https://twitter.com/binaryruse/status/1142318919861981186?s=...