I was working in a hospital doing an hazardous material (asbestos, lead based paint, abandoned chemicals, etc. etc. etc.) survey in a wing that was slated for a full interior demolition prior to a remodel. The place was empty so we got to be pretty destructive with our sampling. We punched a hole in a wall and saw there was a room behind it that wasn't on any blueprints. It was an abandoned pathology lab full of specimens.
I once worked in an office with a room like that, only it was a server room that for some odd reason was walled in on 4 sides, has a functioning light and in all regards with a functioning server. It was found after the new server room suffered a breaker fault but a coworker claimed that the computer he was working on was still able to see the company website, which was hosted on our own server. Tracing the cat5s in the lowered ceiling sent all the wires into what we had always assumed as a wide pillar... it turned out being a room and the servers that were supposed to have been upgraded still running fine.
As for my own scare, I had checked out an wooded area of our lot where suspected vandalism took place last last week
😡, one night a car rolled by, slowed, and stopped
😱oo:, heard some rustling in the wooded area then the car continued on
😱. This is odd because there were no other street addresses on this side of the road until some ways down. Some hours later it was dark out

, knowing my own woods I trekked out in the dark, feeling the trees as I go. Confident no neighbors are out I turned on my flashlight and saw something wrapped in a carpet bag, as I emptied it out it became very clear by the smell and the size what it was, what appeared to be a decapitated animal and its head was, by the flashlight's light, staring at me eerily. I've been around carcasses before, but this caught me completely by surprise, and subsequently embedded it into my mind. The next day when I came back from work I decided to head back in there to see what exactly it is while there's still daylight and I couldn't find it again. The ground littered with feathers shed by fighting vultures, a week later last Thursday I went out and disposed of the carpet bag, which was stained but the smell was more tolerable. I never did figure out what it was, but the eyes reminded me of a husky... white ring black retina, could be because of the flashlight [Seraph P7 on an M3] and the hemoglobin drained head, but I don't know, I'm just glad it wasn't a baby