The twisting corridors and narrow bridges of the Haunted Halls are crowded with foes, creating one of Quake’s most difficult endurance tests. It can get pretty confusing at times, but if you follow the passageways as they open, you’ll have no problem finding your way around. Most of the secrets are located in two main areas, just before the first vore and right before the exit.

When you see the blood-stained grate, shoot it. It will grant you access to this Quad Damage

Secret Area 1
When you come to the three-way intersection over a pit of lava, turn to your right. You’ll see two gratings, one that is covered with blood. Shoot this grating to reveal a Quad Damage and a small bridge leading to it. You may want to wait before you grab the Quad, so you can use it against the first vore.

Secret Area 2
Near Secret Area 1, you’ll come to an elevator near a closed door. As you ride this elevator, step back off of it and run underneath. You’ll fall into a room with 100 health and a teleporter.

Beneath this elevator, just before the sealed doorway leading to the vore, lies a secret area with a 100 health kit

At the top of the elevator there is a Q button, which opens the closed door below. Press the button and jump down. Grab the Quad Damage from Secret Area 1 and go through the now-open door near the elevator. Walk to the middle of the "T" intersection and turn around. Shoot the Q button on the wall, which will open a trap door beneath your feet and drop you into a small cage with a vore. To exit the cage, hit the red Q button on the wall.

Just beyond the hall of nails, you'll see this Q button which activates the elevator. Look up, where you'll see another button. Shoot this button to open a well-stocked secret room

Secret Area 3
Beyond the hall of nails, you’ll come to another vore. Keep him at bay with some rockets, and look up to the left of the Q button which activates the elevator. Shoot the Q button to reveal a room with yellow armor, 100 health, and Quad Damage, all of which will make battling the vore a cinch.

On the bridge leading to the exit, notice this cage on the right. If you jump onto the cage, a door leading to a secret passageway will open

Secret Area 4
Aftedefeating the second vore and activating the elevator, go up. Walk about halfway across the bridge and look down to your right. You'll see a cage with an ogre inside. Jump onto this cage to access some nails and a Pentagram of Protection.