Berlin's Humboldt University — named for its founder, the 19th century philosopher and linguist Wilhelm von Humboldt, and his brother, naturalist Alexander von Humboldt, pictured here — is one of several German universities attracting U.S. students. More than 4,000 Americans are studying in German universities. Markus Schreiber/AP hide caption

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Berlin's Humboldt University — named for its founder, the 19th century philosopher and linguist Wilhelm von Humboldt, and his brother, naturalist Alexander von Humboldt, pictured here — is one of several German universities attracting U.S. students. More than 4,000 Americans are studying in German universities. Markus Schreiber/AP hide caption

itoggle caption Markus Schreiber/AP

Marchers carried a multicolor flag during Warsaw's annual gay pride parade earlier this month. Poland prohibits gay marriage but activists say attitudes toward gays have improved in recent years. Alik Keplicz/AP hide caption

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Unmanned observation towers, funded by the European Union, have sprouted recently along Poland's border with Russia. This one is located outside the sleepy Polish border village of Parkoszewo. Soraya Sarhaddi Nelson/NPR hide caption

itoggle caption Soraya Sarhaddi Nelson/NPR

A group of Afghan women are attempting to reach the 24,580-foot summit this summer. In mid-May, two of the climbers, along with two American chaperones, visited Afghanistan's highest mountain to see the terrain firsthand in preparation for the historic climb. Soraya Sarhaddi-Nelson/NPR hide caption

itoggle caption Soraya Sarhaddi-Nelson/NPR

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

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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

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