Some visitors to the Buchenwald Nazi concentration camp - now a memorial - have gone for sledge rides over mass graves and such abuses must stop, the site's managers have warned.
The site extends across a large wooded area in eastern Germany, as Buchenwald had several sub-camps.
"Cases of winter sports near mass graves, disturbing the peace of the dead, will be reported," the memorial warns on its website.
More than 56,000 inmates died there.
The Nazis imprisoned nearly 280,000 men, women and children at the site on Ettersberg hill near Weimar in 1937-1945.
They were mainly Jews, Sinti and Roma, resistance activists, homosexuals and Soviet soldiers. They were beaten, starved and tortured. Some were used for medical experiments.
The site has a huge cemetery on the south slope of Ettersberg hill, with a belltower at the top - the area now popular for winter excursions.
Rikola-Gunnar Lüttgenau, a historian at Buchenwald, told the BBC that sports activities were already banned at the site, yet "last weekend it was used heavily, many sledge tracks were found on the graves, and the car park was full".
"Now because of the pandemic winter sports facilities are closed in Thuringia [region], so they are using the memorial," he added.
Disturbing the peace of the dead is an offence punishable by a fine in Germany, he said, adding that the memorial has now stepped up its security.
"Unfortunately more and more people have been disrespecting the place, horse-riding or riding motorbikes in the woods."
In April 1945 US troops liberated Buchenwald, where they found piles of corpses, torture cells, a crematorium and emaciated survivors. The Supreme Allied Commander Dwight D Eisenhower said: "Nothing has ever shocked me as much as that sight."
BBC radio reporter Edward Ward gave an account of the horrors of Buchenwald in 1945. You may find some of his description distressing.