A hard place to get to indeed, choose a time thats at low tide with little swell action and little wind, some rock climbing ability is paramount and you need to find the best approach to get there. I suggest you go around the back, seaward side and find the easiest way to get up.
Theres some nasty dropoffs so be extremely carefull taking kids up although we did have 4 kids accompany us up there.
Cache is a pill bottle with log only, BYOP.