Complex sentence: Built in 1969, at a cost of approximately $2.5 million, and opened to the public in 1980, the tower has been a symbol of Seoul and measures in height (from the base) and tops out at above sea level.
Split into simpler sentences: Built in 1969, and at a cost of approximately $2.5 million, it was opened to the public in 1980. Since then, the tower has been a landmark of Seoul and measures in height (from the base) and tops out at above sea level.