Twain's boyhood home in Hannibal, pictured circa 1955, is now a museum. Three Lions/Getty Images hide caption

itoggle caption Three Lions/Getty Images

After John F. Herring by Ken Perenyi, circa 1989. Courtesy of Pegasus Books hide caption

itoggle caption Courtesy of Pegasus Books

MASS MoCA is a complex of 26 renovated 19th-century factory buildings. The site was formerly the home of Arnold Print Works (1860-1942) and Sprague Electric Company (1942-1985). MASS MoCA hide caption

itoggle caption MASS MoCA

Edward Hopper's wife, Josephine N. Hopper, served as his model for 1952's Morning Sun. Columbus Museum of Art/Howald Fund hide caption

itoggle caption Columbus Museum of Art/Howald Fund

Tilman, Arlington National Cemetery, Arlington, Virginia, 2012 Charlotte Dumas/Courtesy of the Corcoran Gallery of Art hide caption

itoggle caption Charlotte Dumas/Courtesy of the Corcoran Gallery of Art

Experts say glass buildings kill millions of birds every year. Scientists at Powdermill Avian Research Center are studying ways to help prevent this. Here, a volunteer tags a black hooded warbler in Rector, Pa., in May. Maggie Starbard/NPR hide caption

itoggle caption Maggie Starbard/NPR

Architect Guy Maxwell holds a printout of his proposed design for the new Bridge Building at Vassar College in Poughkeepsie, N.Y. John W. Poole/NPR hide caption

itoggle caption John W. Poole/NPR