I had a player who want to use some optional class stuff from Tasha's so I had the book open and found myself paging through anything I hadn't gotten a chance to read to see if anything sparked my imagination.

I came to the "environmental hazards" and found the haunted section. I thought it could be interesting to toss in an impromptu haunting as my players went up or down a floor.

Everytine they got to a new floor, they'd here me roll my 2d10 and they'd freak out waiting for the next thing to happen. I'd make sure the hauntings either tied in their backstory (words, phrases or images only their charavter would know and the remaining players would be clueless of, but scared none the less) or tie it to the history of the house itself in some way. Sometimes, if the players were feeling a bit too comfortable, I'd roll the dice but not use any hazard, just to make them think "how is this one going to get us". Anything that had a potential to kill the party I decided to reflavor into something death house related or just ommitted.

I felt it was easy, really effective and even had me excited to see what would happen next.

If you have Tasha's, Id check it.