Visitors to Berlin's main modern art museum this summer should take care not to step on piles of horse manure, placed as a reminder of art that was stolen, destroyed or went missing under Nazi rule.
With his installation at the New National Gallery of four piles of artificial dung, painted blue, Austrian artist Martin Gostner has said he is paying tribute to Franz Marc's painting "The Tower of Blue Horses".
The Nazis seized Marc's seminal expressionist work in 1937, branding it "un-German" and "degenerate". To this day it is not known whether the work was destroyed or hidden away, but it has never been found.
Confiscated Nazi art periodically has reappeared in the decades since World War Two. In 2010, 11 "degenerate" sculptures were recovered during construction of an underground rail line in Berlin.