A rainbow is not located at a specific distance, but comes from any water droplets viewed from a certain angle relative to the sun's rays. Thus, a rainbow is not an object, and cannot be physically approached. Even if an observer sees another observer who seems 'under' or 'at the end of' a rainbow, the second observer will see a different rainbow at the same angle as seen by the first observer.
In these series of photographs, we see the mystified end (or beginning) of a rainbow. Aside from the folklore surrounding leprechauns and pots of gold at the end of rainbows, they are also an interesting phenomena to capture, visually speaking.