Here is a small video I made that shows how to make a ladder in Renegade.
Using RenX to design this (3ds is more stable, but for tutorial purposes, RenX)
Recorded using OBS
A few things to remember, don't forget your collision settings (6:00 min in the video), when you export it, BE SURE to save it was a .w3d (10:00 min in the video) extension.
If you have any questions about this process, you may make them here.
PS: This is a rough example, and the sizing may not be what you desire, although a height of 30 is a close estimate to the height of the Obelisk of Light.