Hardest level in the game in my opinion. Tons of zombies, exploders don't fall at all cost more zombies= bad day.
Follow marker until you reach the church catacombs.
Get the CCTV junction box.
In this area you don't want to fall. There are holes and the like and tons of planks, just be careful. The Spitters are the most dangerous. The Plus side is that most zombies fall into the pit easier then you will.
Eventually you should find the ladder. It WAS a trap. You're screwed.
Where is the ladder