Instructions
Complete the Dark Sanctum's four quests, titled "Peace, Love and Homicide," "Awakening," "Excavation" and "Leverage." This completes the renovation of the building so you can travel through it freely.
Enter the Dark Sanctum. Walk straight ahead to see a large golden statue. Strike the Flit Switch on the bottom of the statue to unlock a door.
Head through the door, located behind the Sacrificial BBQ Pit. The chests in this room contain a priceless gem and a rare piece of clothing, so collect these items, if desired.
Follow the path to reach the Sarcophagus room. Walk to the corner of the room to see the glowing blue Flit Switch. Shoot it to open a door behind you. Turn around and shoot it quickly before the door closes.
Enter the door and go into the new room. Light all four torches in this room to make two Flit Switches appear by the room's exit.
Strike both Flit Switches together using a magic spell. Follow them as they move to the Inner Sanctum. Hit them with magic again if they stop moving. If you do not do this, they will return to their original position.
Continue following the Flit Switches until they break apart into more Flit Switches. Hit all of them with a spell. Go down the stairs and enter the door that opened. Light the four torches in the room to make a platform appear. Cross the platform to open the chest that contains the Tenderiser.