From Valve Developer Community
A prefab located in the Prefabs HL2 folder, containing a complete ladder setup for HL2:SP and HL2:DM.
This prefab includes the following:
- A prop prop_static ladder model covered with a clip brush.
- A (split up) func_useableladder entity.
- Several info_ladder_dismount nodes to provide easy dismounts.
For a tutorial on working ladders, see Working Ladders.