This is the earliest written source we have of the legend. While it only briefly describes the legend (it hardly describes half of the legend as it is today), we are almost certain that at this time, it was very famous. We are not entirely sure about that, but other resources of the time period suggest such a legend was believed. So, without further ado, here is the source:
Many have ventured into many a forest all around the world, in search of a beautiful place. Many have spoken of the world deep inside. We know it exists because, according to another person, “In the woods you will find a beautiful place. A deep wood exists which contains a place that lies in your dreams. To find this, you must spend many months hiking through the trees.” Most are content with this piece of evidence that it exists, but some people, who, in my opinion, are rather stupid (and I’m certain others would agree), don’t think it is sufficient evidence. People in the future, I know, will talk about us, not as people who pursued a nonexistent world, but people who pursued a fact that we were certain about, that we knew existed. We aren’t pursuing something that doesn’t exist. We have enough evidence to support that there is a God in the skies, and we have enough evidence to support that there is a land deep within the woods. We will search and find the land, and we will poster within its boundaries, and we will prevail!