The Hotel Jefferson has been empty for nearly twenty years. This summer, it opens again.

The building at 415 North Tucker — thirteen stories of Classical Revival terra cotta, a full city block — is being converted into an AC Hotel by Marriott on the upper floors and restaurants and retail at street level. Construction has been underway for over a year. Workers have been cleaning original sculptures with dry ice. Restoring the terrazzo floors. Repairing the detailed plasterwork on ceilings that haven’t seen visitors since 2006.

The Gold Room — the jazz age ballroom that was sealed off for seven decades — is part of the restoration. It will open as an event space. The swan sculpture on the stage is staying. The mezzanine is staying. The chandeliers, which survived the decades of abandonment in better shape than anyone had reason to expect, are staying.

The building has hosted two Democratic National Conventions, Sergei Rachmaninoff, Judy Garland, and President Truman. It opened one day before the 1904 World’s Fair. It became a senior residence. Then it was emptied out for a condo conversion that never happened, and it sat.

The restoration is a $100 million project. It’s the kind of thing this city is surprisingly good at — finding something it let decay past the point where most cities would have torn it down and deciding, late in the day, that it was worth saving after all.

The Gold Room will be available to rent. Rachmaninoff would probably appreciate that.