The Alchemist's Haven is a music from the Plague of Shadows soundtrack. This is the theme of the Potionarium, using Flowers of Antimony as a basis. It is Music Sheet #4 in Plague of Shadows and is unlocked by default. It can also be listened to in Sound Test after completing the campaign once.
Music Sheet #4 is unlocked by giving Percy 3 Scrap Sheets.
"Everyone like this song, so play it always!"