Creating spaces, squatting or traveling in Sewers

I've liked the idea for a while. There are little rooms in the sewers that could serve as temporary free spaces to hang out in. The problems with these kinds of rooms is they are for overflow, so if there is rain, the potential for flooding exists.

I've considered using the sewers as a method of travel and have only done so with storm tunnels, but not proper sewers. Not really the best method of travel, but it is a good way to stay out of sight if you need to move in-between spaces without notice.

In Columbus, we don't have underground trains, though I've watched videos of people living in old train tunnels beneath New York City.

I more like the idea of using wooded areas around bridges and train tracks to make a more interesting kind of encampment. While homeless encampments commonly exist in such areas, my thought was it would just be a "periodic autonomous zone" that a group could use for camping, socializing and launching from to put up street propaganda.

I've seen these areas also be transformed to play paintball games or some other purpose. To make these places in-between into something interesting would be fun, though I imagine a specific context would define how such spaces could be used.