This is inspired by various Reddit threads. So post your own, real-life experience. I'll go first. I've had several but I'll tell a few here.
Me and my best friend used to be fascinated with a local cemetery. It's claim to fame is that a notorious killer is buried their in an unmarked grave. Anyway, the cemetery is gorgeous. Lots of roses and other flowers. Lots of old statues. The huge gates at the entrance used to be kept open at night. So my friend and I would drive in there and explore. Well, one night we were exploring and we had stopped the car and had the lights off for some reason. This would have been about 1 AM. I noticed headlights ahead and told my friend that we might be busted. Instead, I see the headlights pull into a mausoleum. The mausoleum is beautiful and was decorated in that faux-Egyptian style and even had a stylized sun disk with wings over the top of it. Anyway, it turned out to be a black limo. Out of the limo exits the driver who opens the door and lets three or four men out. The drive gets back into the car. The 3 or 4 men are dressed in black suits and walk up to the mausoleum, unlock it, and walk in. We freaked out! Our lights were off but we were afraid they would still see us because we weren't that far away from them. So we wait for about 30 minutes hoping they would come out and leave. Nope! After about 45 minutes we decide that we can't sit here much longer and my friend says we need to start the car and casually drive off with our lights off. So we do that. Instead of going down the road that leads right past the mausoleum we decide to take a road we had never taken before and prayed that it led to the exit. Out of nowhere behind us comes a car that had it's headlights off as well. It turns on it's high beams, scaring the shit out of us. The car is riding my bumper. I immediately floored it. We made it out of the gate and that second car, a black car, just stopped half-way out of the gate. We went back a few weeks later and found that the huge gate was closed and locked. Now, every time we go back at night it's closed and locked so we think they did that because of us.
I've include a picture of a similar mausoleum. This is not the same one but this is very close to what it looked like.
As to what was going down, we think it was a secret society of some form or another. Because none of the men had anything in their hands and because they were in the mausoleum so long I think that there is like a trapped door or secret entrance or tunnel there that they use to attend their meetings.