If you've had a long day shopping on Upper Street (and why wouldn't you), St Mary's churchyard is a lovely secret spot, just off the main drag, where you can sit on a bench and rest your weary feet. It's so hidden I only found it recently despite living nearby for seven years. Pass the church on your left, then look for a small entrance through some railings. You'll forget the high street even exists once you're in there. Great place for a picnic lunch.