This plant comes up in my garden every year, in both areas of full sun and partial shade. I call them my balloon flowers because they start out looking like a balloon and then burst into a beautiful purple bloom.
You are not the only one to see the likeness to a balloon. This blooming beauty, Platycodon grandiflorus, goes by the common name balloon flower. As you observed, it grows in full sun to part shade. It prefers a slightly acid well-drained soil and does not perform its best in wet soil. Those adding it to their garden may want to mark its location at planting or in fall as the plants fade. This perennial is slow to emerge in spring and has been the victim of accidental cultivation in many gardens.