Where is collectible #29 in the Darkness?

Answer 1

At the very beginning of the Trinity Cemetery level (I believe after you've fallen from the explosion), you will wake up and walk through a door into an underground maintenance hallway. In this hallway, there is a room you wont' be able to enter, with a power voltage system box inside. If you look through the caged window, on the floor is the collectible you're looking for (I believe). If you haven't unlocked the first Darkness power (the one where your tentacle arm slithers on the ground), you can come back at any point after you've unlocked the power and use it to break through the bottom of the door (vent) and slither through to obtain it.