Milkweed pods in my back alley. When we repaired the cement here, I had them leave little squares of soil bordering the garage door, for planting. I planted climbing roses there (Blaze, which is lovely and does its thing with a couple flushes of roses every year without additional watering, for which I adore it), but the milkweed showed up on its own, and also comes back year after year.
I love the stark urban beauty of this — the prairie is here, waiting for us to let it back in.