This window is about six foot up from the floor in the upstairs shower room. It opens onto the roof, which slopes from the first floor down to the ground floor. The window is often open because we use the shower in there every day.
Mr Perkins can get onto the roof where it's over the ground floor. If you can see muddy paddy-paw prints on the glass, it's because Mr Perkins walks across the glass. Then he comes in the window, running down the wall, covering the wall in muddy paddy-paw prints.
He doesn't just use the window to come in, though: he uses it to get out, too. We found that out when we left him in with the shower room door and window open, and came back to find him outside.
If he comes in through the window, but the door is shut, he emits a loud wail. If he comes in through the window and the door is ajar, he emits a loud wail. He can't open doors.