This institution operates several institutions across the state. The standouts here include the 1911 Cabildo , on the left of the cathedral, a Louisiana history museum located in the old city hall where Plessy vs Ferguson (which legalized segregation) was argued. The huge amount of exhibits inside can easily eat up half a day (don't miss the 1875 Upright Piano on the 3rd floor), the remainder of which can be spent in the Cabildo's sister building, on the right of the church, the 1813 Presbytère . Inside is an excellent Mardi Gras museum , with displays of costumes, parade floats and royal jewelry; and a poignant new Katrina & Beyond exhibit, chronicling the before and after of this devastating storm – a surefire don't miss for truly understanding the effects of this disaster on the city.