This mystery cache can be solved by gathering clues whilst completing my Adventure Lab For the masses - public art in Hemel Hempstead
You will collect 9 numbers, which will correspond to the letters A to I in the following equation
N51 D I.(D-E) A B W000 G H. H ((F-H) + G) C
Envyvatf. Gb gur evtug bs gur ynetr VPG. Ybbx sbe gur svfuvat yvar (cyrnfr ercynpr gur pnpur bhg bs fvtug)