Some 200 works from an art collection in Aachen, Germany, disappeared into the former Soviet Union at the end of World War Two. Parts of these works have now surfaced in Ukraine, prompting a rare exchange initiative.

The exhibition"Phantom Gallery" in Aachen's Suermondt-Ludwig-Museum is unusual and for many visitors, irritating. In part, empty frames hang on the darkly painted walls or black-and-white photographs -- reproductions of artwork whose whereabouts are unknown.

"We are showing pictures, which are no longer here," said museum director Peter van den Brink.

Shortly after the exhibition opened in September, van den Brink received surprising news from Ukraine. German tourists had discovered a number of works of German origin in the Simferopol Art Museum in Crimea. The couple photographed and filmed the works, and handed the complete material over to the Aachen art expert.