I love how travelling forces one to confront all kinds of differences. These can vary from vast and imposing contrasts that force one way out of one's comfort zone while sometimes they can be simple, subtle details that let you wonder at the variety of life.
Personally, I loved this black sand sandpit I found in Iceland. I'm from coastal South Africa and grew up on white sand beaches. Unsurprisingly as a child this white sand always made up the sand pits we played in. Contrast that with Iceland, one of the world's most active volcanic regions, and famed for their black sand beaches. Equally unsurprisingly, this same black sand is also used to fill up sandpits in Iceland.
Its all swings and roundabouts but nice to think about in periods of quiet reflection.