His new book Brundibar is based on a Czech opera of the same name. It was set to music by Hans Krasa, who was imprisoned in the Nazi concentration camp Terezin and later killed in Auschwitz. The opera was performed 55 times by the children of Terezin. Sendak has also written and illustrated the classic children's books Where the Wild Things Are, In The Night Kitchen and Outside Over There. Time magazine has said, "For Sendak, visiting the land of the very young is not something that requires a visa. He is a permanent citizen." Where the Wild Things Are was adapted into an opera, and Sendak designed the sets and costumes for the premiere production. He's since designed several other operas and ballets.