The Haus Fühlingen site was used by the Nazis in World War Two as shelter for forced labourers.
The urban explorers discovered a boiler caked in blood in the basement.
Simon told Reddit he had discovered the boiler while exploring using only torch light, with Simon's flashlight revealing the bloodied basement boiler.
On discovering the scene the two of them fled.
"It was pretty stupid to just go down there without thinking about it," said Simon.
"I think there was just one friend of mine who knew where we were.
"If something had happened, it would have been pretty hard for anyone to find us."
During the war, a Polish forced labourer called Edward M fell in love with the landowner's daughter, with the girl's father having the Gestapo, apprehend and hang the boy. Edward's spirit is now said to wander the mansion still searching for her.
After the war, former Nazi judge Gerhard van K lived at the residence, before committing suicide on New Year's Eve 1962.
And in 2007 a body was found on the first floor of the property, according to the Kölner Express newspaper - an apparent suicide.
Still, nobody knows where the fresh blood came from but it all sounds fucking spooky.
Source : The LAD Bible