I'm glad this didn't just happen to me by myself but was also experienced by my Japanese friend at the time. It was amazing and quite a shock to our systems.
I had wanted to visit Takashima Castle on the shores of Lake Suwa in Nagano Prefecture and finally drove there in late Autumn 2006. After getting lost on the way my friend and I arrived at the small park with dungeon building and moat at around 6:30pm. It was dark and the main building (now a museum reconstructed in 1960s) was closed and locked up. I was a bit disappointed that I couldn't enter and check out the museum but still happy to be there.
I began fooling around. First climbing up the castle wall a little bit (ninja style) then proceeded up the stone flight of stairs to the locked doors of the main keep. I jokingly knocked on the door and gave the handle a tug. Yeah it was locked. I went to get my keys out of my pocket once again jokingly and as I did so my friend took her high heel boots off and ran off back down the stairs. "Did you hear that?", she yelled.
I remember hearing some kind of sound from behind the door but nothing that registered. I gingerly went to the bottom of the stairs and asked what was wrong. Then, from the top of the stairs coming from inside the keep a mans laughter rang out. "Ah ha ha ha haaaa! ". We froze and looked at each other not speaking then back up at the door. It sounded like the voice of a 40ish year old Japanese man. "uh oh" I thought as I waited for a security guy or ground keeper to come out and tell me off. But just laughter I thought was a bit odd.
30 seconds seemed to pass and as we gazed up to the door suddenly from very close (no more than 3 metres in front of me) and from thin air on the stairs again loudly, "Aaaaha ha ha haaaaa". Adrenaline kicked in and I grabbed my friend and said "run run run". We ran on jelly legs in the opposite direction, my friend almost in tears from fright. "Gomenasai!" (I'm sorry!) I said aloud in a shakey voice as we passed through a gate out over the moat bridge.
Then as we stopped for a breath once more seemingly from a top window the keep. Another burst of laughter. I was glad he or it hadn't followed us but my friend was pretty damn scared and so was I. We got back to the car and drive off with one memory we'd never forget. As for me, more respect for old sites full of bloody and violent history.