Translation: The vision of the Tree of Life, also known as Lehi’s dream. (And, in case you couldn’t tell, the castle stands for the Great and Spacious Building. The story can be found in 1 Nephi 8.
1 Ne. 8:2 – “And it came to pass that while my father tarried in the wilderness he spake unto us, saying: Behold, I have dreamed a dream; or, in other words, I have seen a vision.”