This should unlock in conjunction with the following achievement:
The Randomazzo is the first Relic found in Gallo Tower by essentially walking straight north. It essentially allows bonus modifiers to each of your runs (Referred to in-game as Arcana). By now you should have the Milky Way Map from Dairy Plant to have the precise coordinates and can pause the game to view how close you are at any time. In my playthrough there were a bunch of wizards guarding it and they each had lancets which slowed down movement on top of offensive spells so I would recommend levelling a bit before getting to the area.
For reference: Gallo Tower is unlocked by getting to level 60 with a character on Dairy Plant.
Dairy Plant is unlocked by getting to level 40 with a character in Inlaid Library.
Inlaid Library is unlocked by getting to level 20 with a character in Mad Forest.
Sidenote: this achievement is technically tied to the Arcana that is unlocked for finding the Randomazzo, which doubles healing and adds an AOE burst whenever you pick up a healing item.