- "Good old Under. Hasn't changed since old George V"
- — Arthur Hastings on the Wellington Underground
The Wellington Underground was the expansive underground subway system which once connected all of the holms of Wellington Wells together. In addition to that, it served as the city's primary connection to the rest of Great Britain, with the train tracks being connected to the rest of the British railway network via the Britannia Bridge.
During World War II, parts of the Wellington Underground were used as air-raid shelters to protect the population from German bombing raids. During the German occupation, use of the Wellington Underground was heavily restricted and the train was appropriated by the occupational authorities to transport people and materiel between the city and the rest of Britain. One such instance was the Authority Project, where every child in Wellington Wells under 13 years of age was loaded onto a train and sent to Germany as hostages, never to return.
After the end of World War II and the end of the German Occupation, the subway system fell into disuse, disrepair, and finally into ruin. The stations in Hamlyn Village were converted into Motilene distribution nodes, while many of the ones in the Garden District were appropriated by Wastrels and converted into makeshift Shelters, as seen on Lud's Holm. Others were left completely abandoned.
Despite its decayed state, the subway is of great value for the player. Many of the stations include living quarters for workers which serve as shelters for the player to use as a place of refuge. These shelters come equipped with Pneumatic Stashes (which the player can use to store their items), Beds (allowing the player to sleep safely to rest and recover) as well as Workbenches and Chemistry Tables (for any and all crafting needs).
In addition to that, due to lack of any train traffic, the rail lines are fully traversable, allowing the player to use them to quickly, safely and easily fast-travel across Wellington Wells.
- Some of the Stations have items and unique enemies in the fast travel tunnels despite the fact the player cannot access the tunnels without no clipping to get to them.
- Two notable things are a piece of rotten meat in the Lud's Holm station and a rat in the St. George’s station which is classified as an enemy and will instantly kill the player when attacked even if invulnerability is activated.
- The Station in the first holm is the only station with its own unique skybox.
- In all of the stations apart from the Barrow Holm one, the checkered floor expands past the walls to form a perfect square.