setpos -3462.541992 -4757.015137 -3406.053223;setang 49.190102 -65.339981 0.000000This is more of an exploit rather than a glitch because this isn’t possible without using props but it is definitely possible to recreate on default settings. Basically, by stacking 3 barrels up on top of the railing here, you can jump across and skip a portion of the level and get to a load on the other side of the jump.
Seem a little hard? Feel free to try for yourself.
https://www.mediafire.com/?4nias0nz5ymbbvc
What I Would Suggest
Add a player clip brush to the edge of the railing to prevent being able to land on the side of the platform like in the third picture.