This dainty plant showed up as a welcome volunteer in my garden. I’d grown the species, Campanula rotundifolia, in the past, and a seed must have survived. It occurs (sparsely) naturally across the British Isles and on terrain like Switzerland, the Canadian Rockies and Mt Rainier National Park. It does very well in our moderately moist gardens, and the varieties range in height from a few inches to… well, this one is knee-high and growing. Sometimes white specimens occur.
Incidentally, my original plants came from a nursery. I do not recommend collecting in the wild.