Kitchen window. About 2x3 metres if I remember right.
We had a trampoline in our backyard, outside the kitchen so mum could watch us while cooking or whatever. There was a huge hill (our house was in a bit of a mountainous area), and we decided to throw some rocks down the hill and bounce them off the trampoline… but we were uncoordinated 10 year olds so we missed every time. And it was just a bunch of little stones gathering in our backyard.
Then I found one rock. Pretty big, had to lift it with two hands and shot-put it down the hill. That was the one that we finally landed on the trampoline. And it bounced right through the kitchen window.