Secrets of the Gateway Arch! The Gateway Arch became a national park in 2018. At 91-acres, it’s our smallest national park.It’s the tallest manmade monument in the US measuring 630 feet tall and 630 feet wide — only second in the world in height to the Eiffel Tower.To get to the top of the Gateway Arch, you climb into an elevator cab the size of an industrial washing machine, which you share with four other people, and enjoy the 4 minutes to get to the top.It was originally built as a memorial f