Inside the rotunda of the Tehran Museum of Contemporary Art, a circular walkway spirals down from the street level, like an underground version of Frank Lloyd Wright’s Guggenheim Museum in New York. A series of galleries branches out from there, giving up astonishing secrets from one of the finest—if forgotten—collections of 20th century art in the world. A show this fall included abstract expressionist paintings by Kandinsky, Motherwell, Pollock, Rothko, and Stella, to name just a few from the museum’s vault. Sculptures by Ernst, Giacometti, Magritte, and Moore are on permanent display in the garden. The corkscrew-shaped foyer wraps around a giant Calder mobile—its playful red shapes glinting in midair beneath the stern glares of Ayatollahs Khomeini and Khamenei in portraits above.