The famous stone walls which act as boundaries between two fields in Scotland.
I am not sure if you can see the difference in the water but this is the place where Ganges and Yamuna meets in Allahabad. Even though they meet, they still retain their nature, one is calm and other is very wavy and that by itself looks like a boundary that they both dont want to cross.
Now for something which looks like there is no boundary to it at all. Yes, the great Grand Canyon.
“I like geography best, he said, because your mountains & rivers know the secret. Pay no attention to boundaries.”
― Brian Andreas