Workers have made quick work on dismantling Alexander Calder’s Universe sculptural installation from the lobby of the Willis Tower this week. The colorful artwork, which has been a fixture of the iconic supertall skyscraper’s lobby since 1974 is being removed to clear the way for updates which are a part of a $500 million renovation for the tower.

Local preservationists had sounded the alarm about protecting midcentury public artworks earlier in the month when Preservation Chicago unveiled its latest list of endangered buildings. With the sale of major buildings comes repositioning efforts from new owners to modernize and increase value and Blackstone Group, the New York-based private equity firm that paid $1.3 billion for the Willis Tower in 2015 is looking to make major changes to the building. Major items include an updated lobby, changes to the observation deck, and a new 300,000-square-foot retail and entertainment space starting at the ground level.

However, the modernization of the Willis Tower’s lobby doesn’t include Alexander Calder’s large mobile. As workers continue removing the final pieces of the installation, details about its future and where it will end up remains largely uncertain.