I had launched my hang glider off Haleakal, the 10,000ft volcano on Maui. From launch we gained a bit of altitude and flew out over the island and gradually drifted down through 4 layers of clouds. As I approached the highest cloud layer, the sun shining down from above me cast my hang glider's shadow onto the clouds below. When that happened, it created a circular rainbow around my shadow. I know the physics behind it but it still felt pretty magical!
You can read how they happen on Wiki here:[link]