Visit St. Clement’s Island Museum to commemorate a forgotten tragedy of the Civil War, the Black Diamond Disaster. On April 23, 1865, 87 lives were lost when the Black Diamond was hit by a steamer in the Potomac River near St. Clement’s Island during the hunt for John Wilkes Booth. Visitors can take free water taxi rides to St. Clement’s Island and free admission to the museum both days. Details: www.visitstmarysmd.com/.