Another unusual situation you could use for a really special place is a bidirectional river. The one I can think of, the Tonle Sap in Cambodia, doesn't look like a violation of the River Laws on a map. Bidirectional: crazy? No - the "water flows downhill" condition is met differently at different times of year. In its highest flow during monsoon, the Mekong's surface is enough higher than the rest of the year, that the nominal level of the Tonle Sap lake is lower. Flow goes westward. At low flow after monsoon season, the Mekong goes back to being lower than the Tonle Sap, and flow eastward resumes. It's like an immense overflow safety-basin. Plenty of oxbow lakes on seriously meandering rivers do this during flood times; the Tonle Sap is just a huge version, at maybe 100km of 'reversing' section.

At least in this case it's not a purely graphic feature - you about have to have some text to explain it.