I'll never forget accidentally discovering it several year ago. My wife and I were driving around one evening in Westmount, lost but enjoying being lost, when we pulled up to this spot:
https://www.google.ca/maps/@45.49118...7i13312!8i6656
Not knowing where we were, it seemed like some kind of lookout, so we got out to have a look. We turned the corner and still didn't know what it was we'd encountered, but a door was open, so we went in. And while that was quite something, it was only when we went out the front doors that we understood the magnitude of what we'd stumbled across.
Serendipity. I've always sworn by it.