At the start you find a gate with squares.
H=horisontal number of squares, V=vertical number of squares.
The final cache you find at N57 41.NNN, E011 58.EEE
NNN=893+(2*V)-H
EEE=421-(3*V)-H
The cache is somewhat greater than a film canister.
You can check your answers for this puzzle on Geochecker.com.
