Hidden Trapdoor
Firstly, can we just say how amazing that space looks?! Apparently, the OP was helping their dad move into their new office when they discovered a trapdoor just like the ones we see in the movies. So, of course, they had to check it out.
They were surprised to find a dungeon down there with all kinds of forgotten things. While the space can’t be used as-is, we think it can be transformed into an amazing activity room once it’s cleaned out and set up. They could also just use it as a storage room if they want. Either way, they got a pretty awesome deal on that office, right?