My son decided Mercer Island should be Treasure Island too, so we hid this cache up in the hills above Lake Washington and filled it with pirate's booty.
The hide is in another one of the great open space preserves on Mercer Island. The trail was recently upgraded and winds up through some beautiful old-growth trees along a seasonal stream. You could probably do a roundtrip cache hunt by hiking to this cache and then continuing on via Island Crest Way/53rd to "Maddies Treasure Box". See here for trail maps of both areas.
Cache is a small plastic jar containing your typical pirate plunder.