Fortress is a Half Life 2 map designed to create the most economical use of space. The entire map is built around a single pillar in the center, around which the player's path radiates. Initially inspired by much of the level design from Dark Souls, the space was designed to be cyclical and compact with many areas overlapping and flowing into one another smoothly.

When beginning the development of this map, instead of designing it on paper first, I gave myself a large piece of simple geometry in the center of the map and built the major areas of the map around it. I felt that by designing the map this way, I created a more realistic space. Additionally, this helps the environment feel more organic.

Verticality was a major aspect of the map's design. I wanted the player to content with enemies both above and below them, and as such, much of the environment is built around funneling the player upwards, while enemies are spawned behind them. The highlight of this principal is during an encounter at the highlight of the map, where the player must cross a bridge while enemies below fire at them. Another major pillar of the map's design is the treacherous environment the player is thrust into. Instead of relying on enemies to make the map challenging, I instead created a vertigo-inducing environment, and populated it with enemies that complement that design choice.