This former nursing home.
It's a weird place as the upper floors are all tagged and filled with trash and junk and other detritus but the first floor is absolutely mint and untouched and extremely grand.
This one had an interesting end as the extremely vigilant local residents who live practically on top of this building managed to work out we were inside and called the police on us. After shooting the lower floors with the police and disgruntled locals waiting for us outside we decided to leave via the front door, and discovered no fewer than four police cars and many police officers waiting for us. After they asked what we were up to one of them wandered off to check our details and we got chatting to one of the younger officers who seemed genuinely interested in the sort of stuff we were doing, and even told one of the disgruntled locals to stop recording us haha. The officer doing the checking came back and asked the officer we were talking to if he was OK to let us go and of course he said yes, and wished us luck on our next adventure!
A whole string of small bits of luck came together on that explore as it could have ended very differently had we been forced to use the extremely awkward way in to exit the building.