So today I stumbled into a bit weird of a mod for Half-Life 2 called Elevator: Source by PixelTail Games. It is marketed as a single or co-op "elevator experience". What this means, is that the whole mod is based on an elevator, which takes you to 28 unique floors. And oh man, it is quite a journey!
Below is a video of a group playing it for 45 minutes. I know it sounds long, but I have short attention span and for some reason I just had to watch the whole thing!
You can download the mod on the project's website or ModDB. Please note that you will HL2: Episode Two and Garry's Mod 10 and up.