The Auschwitz memorial on Wednesday urged visitors to stop posing for photos on the railroad tracks outside the former concentration camp.

A number of tourists have recently posted photos of themselves balancing on the tracks outside the Auschwitz Memorial Museum, the museum said on Twitter.

“When you come to @AuschwitzMuseum remember you are at the site where over 1 million people were killed,” the museum wrote.

“Respect their memory,” they added. “There are better places to learn how to walk on a balance beam than the site which symbolizes deportation of hundreds of thousands to their deaths.”

It’s not the first time social media photos at the memorial have caused controversy.

In 2014, Breanna Mitchell, a young woman who took a selfie at the memorial and posted it on Twitter with a smiley face emoji, drew outrage from other Twitter users.

“How can you be happy and smile in this pic? Do you not understand the horrors and murders that happened here? I’d be crying,” one Twitter user said in response to the selfie.