Before we get started, please refer to this discussion from gm_boreas:
https://steamcommunity.com/workshop/filedetails/discussion/1572373847/2843417619896858248/

See the changelog.

Sources of November 11, 2024:
https://drive.google.com/file/d/1SipdbZcp0hBg-lIOZlbQZm8nmU5vau8Q/view?usp=sharing

Sources of May 10, 2024:
https://drive.google.com/file/d/1aaPqzaii0Vq29zzuecTC84WaQnp6v4zE/view?usp=sharing

I use Hammer++[ficool2.github.io] instead of the basic Hammer, as there are more tools in it and is more powerful.
Since April 21, 2024, there's a new version for the x64 branch of Garry's Mod - this is the one I currently use (seem to work quite well on gm_boreas). If you prefer to use a previous version, read How to use Hammer++ with Garry's Mod[github.com].

I used to use the custom compilers provided by Blueberry_pie (from the sources), but they don't seem to work anymore. It may be broken by a Garry's Mod update, or maybe doesn't work for a x64 architecture. I haven't looked into this in depth.

Surprisingly, about 20 minutes only to compile the map in LDR + HDR (without -final parameter) on a Ryzen 5 3600X processor!

I created a dedicated software called BSPIntegrator[github.com]. The Vide tool was very unstable and was missing some files. Of course, feel free to use the software you want to use.

I used the exact same arguments given on the discussion.

This folder contains some models I edited for the map. I used Blender[www.blender.org] with the Blender Source Tools[steamreview.org] plugin.
I also used Crowbar, which is really useful to convert .mdl files to .smd (and vice versa).