Fun fact, this actually opened up as an ibis aviary, according to @Toddy's thread on Copenhagen's architecture. The second floor actually had a viewing blind to view the ibises that students would use from time to time, up until the ibises moved to the flamingo aviary. I wasn't entirely sure how they renovated this exhibit for the gibbons (Google Streetview certainly didn't help matters and it looked like there were no photos online of said gibbons), but seeing what looks to be relatively newly placed mesh in front of what was previously an open-fronted aviary... (and really flimsy looking mesh at that! ), that appears to answer that question.
