In honor of the 75th anniversary of Dr. Seuss’s second book, The 500 Hats of Bartholomew Cubbins, the San Diego History Center has opened an exhibition — Hats Off to Dr. Seuss! — that combines two ‘secret’ collections. Audrey S. Geisel, the widow of Dr. Seuss, has generously opened up the estate’s legendary “hat closet” to allow the public a peek at Dr. Seuss’s hat collection. These hats, along with the Secret Art Collection, a series of works adapted and reproduced from Ted Geisel’s original drawings, paintings, and sculpture, are on display through April 19.