Chicago’s tallest building is about to get its biggest upgrade in years.

The City has approved construction permits for a half-billion dollar reconstruction of the lower levels of Willis Tower (233 South Wacker Drive). Altogether, six floors of the building will be re-done, with half of those being below grade. The tower’s perimeter will be extended all the way out to the sidewalk, thanks to a three-story glass and steel addition. The project was designed by Gensler’s Grant Uhlir.

RENOVATION OF LOWER LEVELS (LL), LL1, LL2, AND LL3 AND UPPER LEVELS (L) L1, L2, AND L3. SCOPE TO ALSO INCLUDE A NEW 3-STORY ADDITION TO BASE OF THE BUILDING AT L1, L2, AND L3 WITH INTERIOR BUILD-OUT . SUPERSTRUCTURE/ DEMO UNDER PERMIT 100696292. EXISTING USES: OFFICE, RETAIL, ASSEMBLY (SKYDECK), & GARAGE.

When complete, the project will add another 300,000 square feet of space to the 110-story skyscraper. That space includes pubic restaurants and shops, as well as indoor and outdoor gardens.