National Museum of Cambodia
The national museum opened in 1920 as the Musée Albert Sarraut. Its four terracotta pavilions hold Khmer works dating back to the 4th century. The highlight is nonetheless the exterior by architect George Groslier, who was an author, historian, and its first curator. The building and its collection suffered under the Khmer Rouge; restoration was funded by grants from the Australian government among others (there's an opening plaque with Bill Hayden's name on it inside). It is worth a visit, but if you saw Siem Reap first, the excellent Angkor national museum leaves it for dead.