Brendan James, 29, stumbled upon Shifnal Cave, Shrops., After a friend read it online.
The Explorer took his 3,000 subscribers on a virtual journey as he filmed himself exploring the cave.
Locals have long claimed that the Caynton Caves were used by the Templars in the 17th century.
Historic England has described the cave as a “cave” and believes it was built in the 18th century – a few hundred years after the Templar Order dissolved.
Brendan said he felt claustrophobic and uncomfortable while in the cave.
The entrance is a small hole under a tree – easy to miss for anyone.
He said: “We entered it, and it’s a little crawl space that leads to a huge sandstone cave.
“You wouldn’t think that in a million years he would be here. “
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Brendan admitted he was skeptical at first.
Even though the cave has been linked to the military medical group, it is probably a Victorian madness.
Brendan said, “There were a few pictures online, but nothing significant.
“But when I went there, it opened my eyes. It was expansive.
“Someone had gone over there and made the effort to make such beautiful sculptures.
“It must have looked flawless when it was first done. “
The cave is covered in graffiti and Brendan also found a photo of a man in a “ritual hall”.
He also discovered a semi-collapsed wall, which raised concerns about the safety of the structure.
He said: “I didn’t think I was claustrophobic, but I was grateful to come out. “
Brendan left the cave after about half an hour of exploring because he said he was starting to feel a little dizzy.