Does anyone know what this structure used to be?

I was hiking today at Patapsco and came across some ruins. There was this MASSIVE staircase (you can see the pictures, but like it had these kinda curved pillar type things on it). It looks like what you would see in a hotel lobby. I have a hard time believing that they just put it there for the ease of hikers. Does anyone have any idea what this used to be? And what happened to it? There are a ton of concrete and brick blocks scattered everywhere which makes me wonder if something was there and got weathered down in a storm or something.

Also, in some of the end pictures are pics of a house-like structure on the trail. Again, it seems very intentional and not something that was put there for hikers. More concrete and bricks scattered about there also. Not super far from that big staircase but not super close either. The top was completely flat except for that big hole you see. There’s some windows on the front and side of it where you can see big spaces of rooms in there. And what are those rooms with the curved walls? It almost looks like where trains are parked at a station. Those rooms are also completely closed off from the other big rooms and there’s only one way in & out. It was near train tracks so that made me think of that idea. Of course lots of people have clearly hung out there but it looks like it was something of purpose before that. It almost seemed like a basement area because it was kinda lodged underground and there wasn’t much clearing from the ground to the ceiling. This is different from the staircase but does anyone know what this might’ve been as well?? It’s on one of the Patapsco trails and I believe it is across the street from that old flour mill that burned down. Would love to know if anyone has any ideas!!