Nephi met the conditions given him by the angel for him to see what his father had seen. He believed what his father said about having faith on the son of God and the power of the Holy Ghost, and he kept the commandments. His desire to know was accompanied by prayer, and as he sat pondering or studying those thing in his mind he was carried away in the Spirit of the Lord (v. 1). The mountain was unknown to Nephi. Suffice it to say that the Lord often uses mountains to reveal his mysteries when there are no temples. Enoch was told to climb Mount Simeon and while there he “beheld the heavens opened, and (Enoch) was clothed upon with glory” (Moses 7:2–3). “Moses was caught up into an exceedingly high mountain, And he saw God face to face, and he talked with him” (Moses 1:1–2). Jesus took “ Peter, James, and John his brother, and bringeth them up into an high mountain apart” and was shown great things (Matthew 17:1–9) “of which account the fulness (we) have not yet received” (D&C 63:21). There were probably many more similar occasions throughout the history of the world.
The sign given to Nephi (v. 7) will be discussed when it is fulfilled (12:6).