Taken from the 3drealms forum

Duke Nukem Editing Project tutorials



Setting up a ladder in DNMP requires certain conditions in your map to be present before you begin.
First, you have to have a map that contains the basic geometry necessary to get Duke from one area of the level to another by climbing the ladder and that keeps him on the same game track(for now, a simple ladder). You must also have the basic elements-player_start, game_track- with area brush box as child, and lights placed so you can see your level when you run it.
No matter which way Duke approaches the ladder(to the side, in the background-or straight ahead on a wall in front of him) you will want to create as a "soft" brush a rectangular brush to place against that wall to actually show the shader of the ladder. I made the dimensions of my ladder-X=64,Z=4, and Y=...whatever your map requires in length.
Once you have your ladder brush placed where you want it, click the shader properties tab for your brush and click the button under 'Texture mapping' and select the 'Locked' option. That way, if you need to clone your ladder brush to put another ladder somewhere else, the shader will remain aligned to the brush. Then click 'Browse' and go to e01/ladder01.shd, click on it and then click OK. The shader probably will not be lined up correctly, so you will have to use the 3D view in Texture mode and adjust the Offsets and Scale until the brush shader looks the way it should.(Experiment!) The settings I used for mine were Offsets-X=33,Y=0, Scale-X=103,Y=100.
Next, you need to insert your area_ladder entity from the entity tree under areas\interactive\ area_ladder. Insert it in front of your ladder brush so that it is in front of the brush where Duke will be interacting with it and somewhere along the length of the ladder. Take Note:(The placement of the ladder entity determines the position Duke is in when he climbs. If the entity is too close to the brush, Duke will not climb, but run in place. If the entity is too far away, it will be obvious in the 3D view as he will look detached from the ladder.) Again, experiment in the 3D view and look closely at my demo_ladders map. Then,(as with most area_ entities, you need to create an "area" brush as a child of that entity to define the area where that entity interacts with Duke AND his game_track. So, click on your area_ladder entity, and then, create a rectangular AREA brush that will be placed, roughly, from the edge of your soft ladder brush and extended into the game_track so that Duke enters or touches that area when he approaches it. And, of course, adjust the length of the area so that it runs the length of your soft brush.
The only settings to make with the actual area_ladder entity are for "type", "perpendicular", which I used to have him climb the ladder on the wall beside him in the background, "with track", which means the ladder is in the direction of the directional arrows on the game track(usually to the right as in my demo), and "against track", which means the ladder is in the opposite direction of the game track arrows(usually the to the left). Then, the top_type, where you can have Duke "Stop" at the top(the only option for perpendicular ladders), or "Climb up", depending on the "type" option you choose.
Make adjustments to the various properties until the ladder works the way you want.
It would not hurt to create a "NEW GROUP" from the hierarchy by right clicking the map directory at the top and naming it Tracks, or Areas, and place your game_tracks and area_ladders and such in there to keep them organized. But do not check the option under the "Areas" group properies tab for "Tied". Please remember when you create new area entities NOT to make them a child of another entity or brush!
I hope this tutorial makes sense to you and that you have success with it! Otherwise check the demo map. 1