From The New York Times:
While most public attention has focused on the aboveground portion of President Trump’s planned $400 million ballroom, what is underneath could prove to be the more complex and expensive portion of the project.
Work crews have been digging in the earth for weeks, ripping out the Presidential Emergency Operations Center, or PEOC, to build something bigger, better and deeper underground. The PEOC, which was built during World War II to protect the president and other top officials in the event of an emergency, was where Vice President Dick Cheney was hustled after the Sept. 11 terrorist attacks, later to be joined by President George W. Bush and his national security teams. Mr. Trump was rushed there, too, during protests over the death of George Floyd in 2020.
The bunker is beneath what was once the East Wing, which Mr. Trump tore down last year to make way for his ballroom.