Find the highest place you can legally stand within thirty minutes

Somewhere within thirty minutes of your door is the highest spot you're allowed to stand on — a car-park roof, a hill, the top floor of a library with a decent window — and you almost certainly don't know which one it is. Go find out. The "legally" part is doing real work here: locked rooftops have ended better afternoons than this. Come back with the one thing you could only see from up there.