4. The Baigong Pipes.
I thought this one would be a challenge, but it's not.
Years ago, I visited Beijing and spent some time at the university there. What struck me about the library was that they had every English language journal available - but the same amount of books in Chinese. I couldn't read Chinese so I could only access half of that library's contents. I was forced to conclude that the students there must know twice as much as me.
All we know about China is what comes out of there translated. In the case of these mysterious pipes, all that seems to be available is one newspaper report.
However, someone with the time and inclination to press this particular matter further has found that the Chinese do, in fact, know exactly what these pipes are.
Fossilised tree casts. Yes, they are palaeontological, not paranormal.