Rainbows are probably my favorite form of "reflection": "Caused by the refraction and dispersion of the sun's light by rain and other water droplets in the atmosphere." (Wiki)
I am very lucky, because I live in Colorado on the edge a special, giant valley which is famous for its spectacular weather events - the West Mountain Valley. Extreme storm can occur at any time and especially rainbows can span their iridescent arcs often during monsoon season in brilliant displays of color.
We are pretty spoiled when it comes to rainbows, but the rainbow in the attached image was most likely the biggest and brightest rainbow anybody has ever witnessed in our unusual valley. Neighbors were actually calling each other to look out of their windows... The entire area took on a golden hue from reflecting the low, setting sun and the width of the rainbow was truly breathtaking. Most of the time people like to show the whole rainbow from side to side, end to end. But this time I actually zoomed in on the lower part of the rainbow and even included a house (bottom right) into the image - just to give a feeling of the unbelievable size of this rainbow. And the fact that there was a cloud moving through/behind the rainbow made the entire experience even more breathtaking.

Equipment: Nikon D810, Nikkor 28-300mm/f:3.5-5.6, B+WXS-Pro Pol-Filter

Camera settings: Lens at 190mm, f/7.1, 1/200 second, ISO 200