For a number of years, we were pretty active geocachers. "pandandfoo" as we were known - though it's been a while since we did anything much.
We started hiding caches, and I started devising puzzles to conceal the coordinates -- a popular variant of caching, at least in these parts. This is one puzzle I was pretty proud of. People are still busting their skulls on it to this day.
I called it QMXLP
The posted coords are for parking only
ADDGG FXDFG AVAAD DAGXA AGAGD XVVDG FXFGG FGXAA AGDFG XADXG AXDVD GXGFG XFXGX GDGGV ADDGG VDGAF XFAGX FDDVG AGAGA AFAXA DAAFF GXXAA AXXAA DGFGG GGGGA GAGAG AGAGA GAGAG AGAGA GAGAG AGAGA GAGFA AFGAD DAGDF DFXGX GAGFA ADDVD VGGAV DAGAX GXDGA GVDAA AGAAV ADFAG AGGGF XFDGF GAAXD DGAAA DGAGD GAAFA GVXXX AGAGG XGAFX XFDDX XAGXF DADGA XXAAX GGGXX DXXXG XGADX AXFFD XVDXF VAADD ADDAD XXXXG DVAGA XAADA DVAGD VXGAG AAGAX GXADX XXXXX XXXXX XXXXX XXXXX XXXXX XXXXA AGXDX AAFAG AVGFA DAFDD DFXXD GGAAF GFGAA AFGAG AFXDA AGXFD FDDAD AAAAA AFFAX DVGXD AAFAG AVFDX DDGAA AFAXF XAVDF AAXFD DAXDD AGGAA FDDAG DGXGD XDDAF GXAGD VAGGG XFXGA GFFXV ADDGD AFAGG VAAVX VXDAF GXXFG DAGFA DFXXV GAADX DXADA AAVXV XVXVX VXVXV XVXVX VXVXV XVXVX VXAFX XGGAA FGAVF XDGAA AFVAF ADADD FADXD FFAFG GDDFA AFGAX AGVGG AFAXA ADADA AVDVD GGGGA GVGFX DXAVA AAAFD FDVDD AVAGX XGADA VGAFA XFAGA DVAXA FAGFG XFDGD AAXAG AAAXF VAXGX GDAXX FAGAF DFGAA FDDXA XADDD XVGDF DFGFG AGXAG ADDAV FGVDF ADXAX AXAXA XAXAX AXAXA XAXAX AXAXA XADGG GAGAD GXGVD AAAGV AFADA GAADX DDVAA FAAAD AAAAG XAGDX GGAXF AADVG AFGFG XXAAD ADAAA AAGGD GDAAA FFAGA AXAVD VADXX XDAGD GDAGG VGGAG AGDAX XDXXG FXXGD DXVGX AFFAF AGAFD FAFDA XXDAG VAADD GXVXV GAGXV XDFVA GGVDG AAXAF AAAAA AAXAD XVXVX VXVXV XVXVX VXVXV XVXVX VXVXV AGAAG VVDXA XFADD GAVAD GDADG GGAAA XDFAD AAGAG AAXAA AGADF ADAFG AGXGA AAAGA DAVAF
I only ever gave out one hint for it, which I will replicate here. (Putting it in ROT-13 in case you want to go at it "pure") Gur vasbezngvba lbh arrq vf ivfhnyyl qvfgvapg vf gur cntr.
If you want more stuff like this, let me know.
By the way, one person solved it with a pure cryptanalytic approach, not by sussing out what the keys are. I've heard of the "greater fool" principle. Apparently there's a "greater geek" principle, as well!
"It pays to be obvious, especially if you have a reputation for subtlety."