They no longer allow visitors to the undercroft, as far as I know, but there’s some good photos of it here:
https://architectofthecapital.org/posts/2016/7/30/underneath-the-lincoln-memorial
They no longer allow visitors to the undercroft, as far as I know, but there’s some good photos of it here:
https://architectofthecapital.org/posts/2016/7/30/underneath-the-lincoln-memorial