Under what was formerly the city of Toronto there were a number of Subway Train tunnels and civilian pathways that crisscrossed under the city. While portions are claimed by squatters, much of it has been reclaimed as is being slowly refurbished to be a civilian shipping area as well potentially a transit system in addition to a place to flee too if necessary.
Many of the areas below the city seem dilapidated to a degree but are quite safe. Many people have actually taken to making the area look "cyberpunkish", a style from the early 21st century that was envogue. Other areas are up to modern standards however.