In a city where unusual is the usual, it's hard to come up with something that would be considered provocative. San Francisco's got plenty of whimsically educational museums, like the hands-on playtime that defines the Exploratorium. But nothing beats an unflinching look at the physical and psychological aspects of sheer brutality. What we are truly short on are museums that also educate on the unpleasant aspects of history that must not be repeated, such as the Museum of Tolerance in Los Angeles. Doing its part to make up for this void is the 7-year-old Chinese Holocaust Museum, a converted Sunset District storefront that is open on weekends and by appointment. Given our current world climate, there's valuable insight to be gained from examining relatively recent history such as this museum's main focus, the late-'30s to mid-'40s period referred to as the Nanking massacre or, in the title of late Bay Area author Iris Chang, The Rape of Nanking.