The key to its entry is theft. It must be illegally found. Fraud is acceptable. On the night of its theft, hang it on the north wall of a moonlit room. The woman in chains will turn and ask for help.
https://scottjbennett.com/ttrpg/dnd/motbm/map
Infinite broken night. Milky alien moons. Wavering demons of gold. Held in this jail of immortal threats are three perfect sisters…
https://www.sffworld.com/2016/07/maze-of-the-blue-medusa-zak-sabbath-and-patrick-stuart-interview/