“Visitors new to the National Gallery of Art’s East Building might not detect any sign that it has undergone a major renovation. The galleries of the I.M. Pei-designed modernist addition to the National Gallery have been closed for refurbishment since 2013. On Sept. 30, they will reopen with 12,250 square feet of new exhibition space, two new stairwells creating improved public flow through the galleries, some 500 permanent collection works on display (up from 350 before the redesign), two new sky-lit tower galleries devoted to giants of 20th-century art, and a new open-air sculpture terrace along Pennsylvania Avenue.”