Back in 1999, a classmate told me about a "secret cave" behind Bill's house in Pokemon Red/Blue and the necessary entry conditions. I remembered his story and conducted some research more than two decades later. I discovered his "cave" story was similar to the Bill's Secret Garden legend, but it seems like his version was somewhat unique. In any event, my article discusses the story I heard and the more common versions I found through research.

https://thenewleafjournal.com/bill-secret-garden-pokemon-urban-legend/