Whats the one thing the City Museum (701 North 15th Street; 314-231-2489 or www.citymuseum.org) is missing? If you answered, A 1924 Wurlitzer pipe organ, youre fortunately mistaken as of Tuesday, July 31. Formerly of New York Citys Rivoli Theatre, the organ in question (lets call it the Toasty Rivoli) has been lovingly restored and outfitted with an electronic controller for the continuous musical accompaniment of all your City Museum adventures. (But we would greatly appreciate it if the controls were bypassed for a lengthy session by Ernie Hayes every once in a while.) Check out the gigantic, swinging organ today or any day thereafter; admission is the standard $12, and doors open at 9 a.m.