I always find these threads when it's late. Oh well.
I've been doing wildlife work for most of the past 10 years.
Weirdest thing I found was on a military base. In searching for my target species, I had pretty much freedom to cover 90% or so of the base. One day, I found this pit that was partially covered with old logs/sticks. Old enough to be rotten, which is why it was partially covered. Inside, I found what looked like two long guns. Freaked me out a bit, until I pulled them out and notice someone had taken crutches and basically taped them up with wood to look very convincingly like actual guns. And this was in a place where basically no one went. Military surely didn't train on that particular spot. But there were always stories about the people who had second thoughts and would try to just run away.
While at my first field job, my house was on the property with a few other employees living in adjacent houses. One day, while in bed, I heard a voice in the wall. No other way to explain it. Couldn't make out what it was saying. It was coming from a wall in the interior of my house. Between my bedroom wall and the hallway that went by the bedrooms. No roommates and no neighbors outside.
There were lots of ghost stories from the "lodge" at that place. The lodge was Antebellum era plantation house. I never really had a ghost experience myself, just the voice in the wall.
Another time, I had just found this endangered species that had never been documented in the property. The next night, people come out to try to find more. As I work extremely slowly to approach and capture one over a period of 3 or 4 hours, a buddy is keeping his feet dry and just watching me do my thing. Or so I thought. He claimed he was watching lights dancing on the horizon most of the time. Of course he didn't tell me anything until later that night, and I guess he was someone I knew to make some stuff up.
The real creepiest thing that ever happened to me was a nightmare. I had this nightmare while I was camping, and I was dreaming I was camping...where I was actually camping and with the people I was actually camping with. In the open, in our sleeping bags, on top of a tarp at the beach. But raccoons were coming out and scratching at my head. I realized I was dreaming, but couldn't even scream to wake myself up. All I could muster was moaning. The next morning, my friends asked me what the hell I was moaning about all night long.
This one really doesn't have to do with the wilderness at all, but as a teen I had my girlfriend and our mutual friend over after a night out while my parents were out of town. Shortly after we walked in the door, the phone rang. It was a 911 operator doing a callback after someone called and hung up. There shouldn't have been anyone home.
Oh, and I found what might have been human bones while doing wildlife surveys. Walked lots of ground that had heavy history going back to when Native Americans roamed as well as a hotspot around Colonial times. It was embedded in a pile of oyster shells, so it could have just been something like a deer or hog.
And for a different kind of creepy...one night just about 2 years ago, I was going out after dark for some survey work in a national forest. I found this staircase. Didn't go anywhere or connect to anything. I had no one with me, and I was never able to find it again. I feel like it was probably 30 ft tall, so maybe it was an observation thing that got abandoned.
Earlier that same year and in the same NF, I was walking out to check another survey site and was just walking along until I remembered to look and make mental notes of landmarks to navigate back to my car. When I looked up, I saw about 4 pairs of eyes shining back at me. I was still, they were still. All I could think to do was try to intimidate them, because they were likely deer. I clapped my hands. Not a flinch. I remember the hair standing on the back of my neck and I just made this guttural growl-yell as I lunged at them. They scattered, but slowly as if they were just going to regroup. My only guess is that they were coyotes. But that would be the only time I've ever witnessed coyotes being together, if so.