Most Likely A Cistern
With the help of some friendly YouTube comments, Cyrex686 learned that the secret room may have been a cistern, a tank used to hold water, that was used when the building was an industrial factory over a century ago. Cisterns were widely used before indoor plumbing was invented. Cisterns would collect rainwater and store it in a tank for later use. The strange line-marking on the walls were actually from rising and falling water levels. But why had it been mysteriously sealed off?
Most Likely A Cistern
Essentially Useless
The cistern could be put back into use, but modern technology rendered it essentially useless. Many people commented that in older buildings, especially industrial ones, things like cisterns can be found. As they are no longer needed they are simply closed. The cost of removing the cistern would have been much larger than just closing it off. Cyrex686 was also lucky that the pipes that he uncovered weren’t filled with liquid sewage or something equally as disgusting and dangerous. Had the cistern leaked, it then could have flooded the entire place with aged dirty rainwater into. So now what would he do?
Essentially Useless