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From HalfLife 2 Knowledge Base

EDIT by SixThree

Note: The below tutorial is for HL2 ladder creation.

To create a ladder for CS:S, create a prop_static with a ladder model (props_c17). You can also create a brush-based ladder using a simple brush and a ladder texture. Anyways, infront of the object/brush you want to be climbable, create another brush as close as you can to it, but without touching. Make sure the face is the same width/height as the climbable object. Assign the toolsnodraw texture to this brush and then hit ctrl+T and create it as a func_ladder. Now you have a climbable face which is infront of the object/brush. This gives the illusion that you are climbing a ladder, where infact you are scaling an invisible wall just infront of it.

By omega552003

Step 1:

First Create a new entity called prop_static that uses the model "models/props_c17/metalladder001.mdl"

Step 1

Step 2:

Now make another new entity called Func_useableladder and place it so that it is at the bottom of the ladder.Then click and drag the circle in the center of the func_useableladder and drag it so its bottom is at the end of the ladder. (NOTE: this entity CAN NOT be in the ground or touching anything else or it wont work!)

Step 2

Step 3:

Now you need mount/dismount points. Create a new entity called info_ladder_dismount place these right next to you ladder's "exits" or where you player will be placed when they exit the ladder.

Step 3

Step 4:(optional)

If the ladder is near any other ladders or the ladder moves along with a parented object you should give the ladder a name and have the ladder's dismount points point to the ladder.

Step 4

Testing and Debuging:

Once the func_useableladder entity and its info_ladder_dismount points have been placed, you can compile your map and test it. you can use the sv_showladders cvar to have the engine draw debuging information for ladders in the map, to use it correctly set it to 1 then load the map or reload the map if its currently loaded.