I'm surprised no one mentioned this: FRESH LOBSTER!!!!!
I had a similar layover in June and spent most of my day on Signal Hill walking around and got to see some icebergs.
I also managed to get lost in St. John's trying to find a place that served fresh local lobster and as I was about to give up, I found it!
Not a bad way to cap off a month long trip. I'd love to go back though and see more.
Anyways, def check out Signal Hill. I didn't know where QV was so I didn't get a chance to see it sadly. But always next time!