Beneath the Lincoln Memorial is its "undercroft," a cavernous area filled with rows of tall concrete columns and large expanses of open space that has long been hidden from the public — and soon, it will be the site of a new immersive museum.
On Monday, the National Park Service announced plans to create 15,000 square feet of exhibit space that will explore the history of President Abraham Lincoln and the memorial that honors him.
https://www.npr.org/2023/02/20/1158292427/lincoln-memorial-museum-undercroft