func_ladder
func_ladder is an internal brush entity available in all 
Source games.
When VBSP compiles the map, it converts func_ladder brushes into regular world brushes with ladder contents, and an info_ladder entity is created with KVs indicating the bounding box of the ladder.
In 
Left 4 Dead and newer, the geometry is kept as a brush entity, and converted to a func_simpleladder instead.
Note:This entity doesn't function in 
Half-Life 2: Episode One and newer, even if to added to base.fgd. Use Func_useableladder instead.Func_ladder is still used in
Left 4 Dead series, 
Counter-Strike: Source, 
Day of Defeat: Source, 
Garry's Mod, 
Vampire: The Masquerade - Bloodlines, and 
The Ship: Murder Party.
Important:func_simpleladder does not exist in CS:GO engine branch and Strata Source, and as such, if a func_ladder is used, the brush will be deleted on spawn. Consult Creating Ladders (CSGO) for help.
Warning: Func_ladder brushes are still world brushes, and will create visleaves unless using materials with %CompileDetail or %CompileClip. 
Tip:%CompileDetail parameter can safely be added to 
tools/toolsinvisbleladder.vmt without any negative consequences (the modified VMT does not need to be shared with the compiled map).Alternatively, create a
tools/toolsladder.vmt with %CompileClip instead of %CompileNoDraw+%CompilePassBullets (works in , but not ).Entity description
A ladder. Players will be able to freely move along this brush, as if it was a ladder. If you are using a model prop for the visual representation of the ladder in the map, apply the toolsinvisibleladder material to the func_ladder brush.
This entity has no keyvalues, flags, inputs, or outputs.
Note:This entity is prone to exploitation, as a player can travel up the ladder with two keys at once to travel faster up, and at the end of the ladder they will be flung upwards to possibly reach high areas.Note:This is an internal entity. When the map is compiled by VBSP it is processed and then removed: it does not exist when the map is running.