This is a time-lapse of making the level called “A dream of Katarn”. It was inspired by the hexagon puzzle in Dark Forces.
What is not in this video is the time it takes to actually design the level, drawing on paper first and then building rough levels Blender that look awful but allow testing the concept. After a few (or a lot of) iterations in Blender I generally remake the level from scratch one last time to make sure it looks great. This last step is what this time-lapse shows.