Welcome to the mother of all blank cache! (or 18 ways to solve a blank cache!)
I've the CERTITUDE that google satellite map will help you with the SOLUTION
Additional Hints (To maintain the "blank" look)
Fbzr uvag. Wnzcnpxrq pnpur orqnmmyr pnpuref / -Gevbzcuny ryh. Vy urfvgng ha crh ybatgrzcf
Here a list of some source of inspiration that may help you solve this puzzle: GC6RATP, GC2JWHF, GC7C4YN, GC7D616, GC2NKJB, GC23DVV, GC11R75, GC5E4BM, GC3J3P7, GC3J3PC, GC4AFC5.
Please, don't hesitate to contact me. I really like to help, even on intentionnaly difficult puzzle.