You may be looking for the Choir Entrance.
The Choir was used for torture and contains three rooms, each of which has a different torture device: an Iron Maiden, a Torture Wheel and a Brazen Bull. Extreme methods such as the Brazen Bull were not used to extract vitae but rather to instill terror in the other victims, ensuring maximum vitae could be harvested via other torture methods later on. Pipes run to each of the torture rooms from the entrance, which supposedly carry the screams of torture victims back to the cells in the Nave. These can be used by the player as a guide for navigating the dark, red fog-filled area.
As soon as Daniel enters, Alexander telepathically taunts him about "salvation", blaming him again for all the death and suffering, trying to urge him to abandon taking revenge.
The mushroom for Agrippa's Potion can be found in the Choir. It is located outside the entrance to the chamber with the Brazen Bull.
The Choir is full of Brutes, making it perhaps the most dangerous area in the entire game. Keeping the lantern off is advisable to avoid encounters. Should a Brute encounter ensue, Daniel should not attempt to run -- Brutes can overtake him easily -- but hide and wait behind a nearby pillar for the monstrosity to walk by. Hiding and even running is not too difficult here as the entire area is dark, although these tasks may be difficult at low sanity. It is possible to lure a chasing Brute into a pit, like jumping onto collapsed pillars suspended over the chasm, but one has to be incredibly swift and nimble. 
This is how to move around the whole area without missing any item:
- As you enter the Choir, you will automatically face left. Hug the left wall while walking forward and you will eventually reach the Iron Maiden room. Collect everything, most importantly the Orb piece.
- Exit the Iron Maiden room and move forward. You will pass a bridge to your left. Do not cross it as a monster lurks nearby. Continue moving forward until you reach the edge, then turn right and cross the first bridge you see to your left.
- Collect the items near the rocks in front of you, then move near the wall. Proceed forward while hugging the right wall, and you will eventually reach the Wheel room. Collect everything.
- Exit the Wheel room and continue moving forward with the wall to your right. Once you come to the collapsed pillar, you might hear a Brute growling. Hide for a while until you feel safe, and then cross the pillar to get to the other side. Keep moving forward while hugging the wall to your right until you reach a room with a bunch of mushrooms outside. Break the largest one with your hammer and chipper and take the Poison Gland. Afterwards, enter the Brazen Bull room and collect the last piece of the orb.
- Exit the Brazen Bull room and move forward, still hugging the wall to your right. When you have to choose between going right and going straight, go straight until you reach the edge. Move forward with the edge to your right until you reach a bridge. Slowly cross it and move forward until you reach the exit.
- The player can also navigate the Choir simply by following the pipes on the ceiling.
- The music heard in the Choir is the same music heard in the game's menu screen.
- As Daniel approaches the Iron Maiden, it will suddenly open, a terrifying cry will be heard, and blood will burst from it.
- If Daniel tries to get into the Iron Maiden, it will suddenly slam shut, obviously damaging Daniel's health.
- If Daniel uses a tinderbox to light the fire under the brazen bull then the cry of a bull will be heard and Daniel's sanity will fall considerably.
- According to Thomas Grip, the Choir's thick fog and difficulty to navigate was inspired by Silent Hill.
- Brute's shouting can be heard even if it is unencountered by player, and the closer it is, the more frequent and louder it will be.
- As you make your way back to the entrance when you're leaving the choir, the Shadow can be heard roaring, and bones will fall from the ceiling, this will damage your sanity.
- It is possible to fool a Brute to it's own demise. Take note that at the top of the map there is a endless pit between two ledges. The ledges are connected by a broken column that can be traversed safely to and from either side. When a Brute comes in pursuit, go to this section of the map and stand on a part of the ledge that slightly juts up and out. From there, jump up onto the fallen pilar. Get the Brute's attention if it had lost you. Watch as it attempts to charge and fail in the process. Make sure to keep a safe distance away or else the Gatherer will take you too!
between two platforms
Amnesia The Dark Descent: Brennenburg Castle - Rainy Hall - Old Archives - Entrance Hall - Archives - Wine Cellar - Laboratory - Refinery - Cellar Archives - Archive Tunnels - Back Hall - Study - Guest Room - Storage - Machine Room - Elevator - Prison: Southern Block - Prison: Northern Block - Cistern Entrance - Cistern - Morgue - Control Room - Sewer - Nave - Cells - Choir Entrance - Choir - Main Hall - Transept - Chancel - Inner Sanctum - Orb Chamber