The The Hidden Apartment Building is found in The Hidden City, after being revealed by Earthbound and Down.
A primary stat of 135 is suggested. If your main stat isn't high enough, you'll see the following message:
(It is recommended that you have at least 135 <mainstat> to adventure here.)
- This zone might be too tough for you.
- The Pastamancer thrall Vampieroghi will remove the Cursed effect. Pastamancers should avoid having Vampieroghi bound when attempting this zone.