People stand beside the entrance gate of the former concentration camp in Dachau, southern Germany, on Wednesday. Dachau was opened in 1933, less than two months after Adolf Hitler became German chancellor, to house political prisoners. This week marks 70 years since U.S. forces liberated the camp. Christof Stache/AFP/Getty Images hide caption

itoggle caption Christof Stache/AFP/Getty Images

Poland's second-largest city is also a major tourist destination. Krakow (seen here at night from the Krakus Mound) is suffering some of the worst air pollution in Europe. Arek Olek/Flickr hide caption

itoggle caption Arek Olek/Flickr

Berlin residents Mareike Geiling (left) and her boyfriend, Jonas Kakoschke, speak with their roommate, a Muslim refugee from Mali. Geiling and Kokoschke helped launch a website that matches Germans willing to share their homes with new arrivals. Soraya Sarhaddi Nelson/NPR hide caption

itoggle caption Soraya Sarhaddi Nelson/NPR