Nauthúsagil
Next to one of the most famous waterfalls in Iceland lies this not so famous waterfall. You start out in a dirt parking lot after arriving on a dirt road and walk a pretty non-descript pathway to the mouth of a revine and where the magic starts. You've got to cross a river a few times, several literally hugging the rock wall to not fall in, and scale a smaller waterfall with the help of some chains anchored into the rock. A little further and you come into the chamber where the this waterfall hides. It was such a cool experience having this place all to ourselves so we took our time enjoying it (while also getting very wet). After seeing some of the other massive waterfalls and epic vistas that Iceland has to offer it was so cool seeing this much smaller and intimate one.