Similar to Welcome to the Arena!, we have seen this level back when we were playing Dark Hour. I assume both were in their original form for Aftershock (or closer to original) while Dark Hour was a modified version by Kosta Mousses (who apparently took credit for the levels, as I never saw a readme even though it explicitly said that one needed to exist if this level was to be redistributed or modified).

This level is intended for Single Player as well as Multiplayer use according to the readme, though no monsters exist so it is rather useless in Single Player besides as a tour like we are doing anyway. No differences between the versions exist, though this one has more spawn locations than the Dark Hour variant.

Unlike Welcome to the Arena!, little has changed between the two versions. Textures are of course different, with the actual crypt being somewhat similar in texture (both being rock based) while the first half is entirely different (brown texture with rivets instead of metal). No geometry changes exist. Placement isn't even that different, the main difference is that the player will spawn in Single Player with the Nailgun (while in Dark Hour it was to the right). I can see why this placement change happened, the Nailgun can be quirky (usually, it doesn't seem to spawn with the player if you restart the level).