09/07/2015 - NEW HINT - NEW CACHESIZE
After looking under a lot of big rocks, you finally found a nice box. (see: urban swimming)
And now what?
Laying on the beach is too boring for you? So go on a little adventure! Take on your bathing suit and swim into the cave, you see from the box on the other side of the bay. Too dark to find the box? Bring a torch or just feel for the place where the box could be. When you arrived in the cave you will easily recognize where to look for.