The description is out of date: HL2 Workshop is a thing now.

the part after we jump down the hole is quite hard to realize what to do
the hole is way too small to be easily noticed

Okay, yeah, I figured it out, somehow I missed the crate of grenades.

Ofc that is possible, you just need a stop for a minute and observe what the situations present you with, the map isnt originally for gmod so as it is written in the description " if you fly around the map or start spawning stuff you shouldn't and ruin your experience, sry but that's on you."

Is it possible to beat the map without using noclip? After I jump down the hole, there's nothing I can do, and the only way to go seems to be to go through a hole that's too small to fit through without a resizing addon like the Shrinkinator. It seems the only way through is noclip. While Below the Wind has a similar hole, that's more or less just an alternate route (the room can also be accessed by an air vent with some trickery) but I don't know what's going on here.