The Manukau Coastal Walkway has a low tide route that takes you from Flounder Bay around to Sandy Bay.
Auckland Council maintain some great walking tracks in Gittos Domain and there is a stairway to the high tide track that takes you around to Sandy Bay and beyond.
Flounder Bay is also accessable from the bottom of Lewis Street at low tide.
Cache is at the beginning of the stairs and well camouflaged.
BYOP