The easiest way of going to Grinda is probably by boat from
Stockholm or Waxholm (more info can be found on Waxhomsbolaget).
The cache is a light green tupperwarelike container with a
transparent lid.
After you have searched (and hopefully found) the cache I
suggest a visit to the inn Grinda Wärdshus.
Gur pnpur vf uvqqra haqre n fgbar jvgu fbzr irel fznyy fcehprf nebhaq vg.