You'd be pretty surprised if, on a trip to the zoo, you came across one of the animals just wandering around outside it's enclosure.
But that's exactly what happened to people visiting Belfast Zoo on Saturday afternoon.
The zoo said the chimpanzees made an improvised ladder from a large tree branch propped up against a wall, and were able to climb out.
The cheeky chimps were locked into their inner enclosure after the great escape.
This is the second escape attempt by animals at the zoo. In January, a red panda called Amber went missing from the zoo overnight before being discovered in a nearby garden.
One family saw a chimpanzee on the path in front of them, while several other chimps remained on the enclosure wall.
Danielle, from Holywood, was at the zoo with her two children Grace, 8, Leo, 6, her partner Dean and his 4-year-old nieces Summer and Willow.
They filmed the entire escape from start to finish, and Ms Monaghan said although they were scared to begin with, the chimp "wasn't aggressive".
She said: "It made us feel at ease. We just walked past it and it was absolutely grand," and added it was a day she would "never forget".
Alan Cairns from Belfast Zoo said: "We think what has happened is that the trees in their enclosure have been weakened by the storms and so they've been able to break them and use them as a ladder to get out.
He said the zoo's chimps were "quite cowardly" so went back into their enclosure themselves during the incident.
"They're intelligent primates and know they're not supposed to be out of their enclosure, so got back in themselves," he said.
Belfast City Council, which runs the zoo, said one chimpanzee "briefly" left its enclosure.
A spokeswoman said: "Zookeepers were present as the chimpanzee quickly returned from an adjacent wall to the rest of the group inside the enclosure."
So what's the zoo planning to do to make sure it doesn't happen again?
Mr Cairns said: "We like things to be natural in their enclosure, to have trees in it, but we will review it.
"We may have to remove the trees or make them a smaller level, although we don't want to do that."