If I could go back in time I'd find out when they built this room and I'd come knock on the door. I'd ask them to please clean the dirty barn wood before they put it up as walls. I'd remind them that someday they'd die and someone else would buy their house. I'd tell them that it would be nice, for that person, if they'd take the time to clean the boards.
And while I was there I'd tell them that wallpaper is a bad idea, cats are really bad with carpet and that the heating system they put in their addition was put in backwards and that they should fix it because otherwise the one part will sound like someone's banging on the doors all night long and the upstairs section sounds like there's going to be a flood. I might just throw in the fact that they should probably get a new boiler system for the older part of the house because it's going to leak like crazy.
So yeah, I've been a little busy cleaning these disgusting barnwood walls. I have to change the rinse water after every single board because it's black. See the before and after in the picture?
You know the saying, "If these walls could talk"? Well, if mine could talk, they'd moo.