This cache, which should be a fairly simple find, is hidden at the southern tip of the Sibley Peninsula.
If you are able to arrange water transportation to the site, your travel time (and effort) will be greatly reduced, but why not take the opportunity to spend a good long day hiking, or even do an over-night camping trip to nab this cache.
While geocaching is not permitted within Ontario Provincial Parks (except under strict guidelines) this cache is not within the park boundaries. Never the less, most cachers will want to take the Kabeyun Trail starting near Silver Islet, hiking past the Sea Lion, Tee Harbour, Lehtinen's Bay and across the foot of the Giant. The last 750m will take you outside the park to the observatory.
Hiking this route will require a steep climb up and over the foot of the Giant (250m) and about a kilometer or so of scrambling through large talus.
If you visit this cache between May and September, you will probably meet up with the "bird people." Thunder Cape Bird Observatory is manned during the finer months and there is lots of activity you can join in on in the Spring and Fall. Be sure to volunteer to do the "happy clappy" and take a visit to the observation tower while you're there.
PS: If you think this cache deserves it, I'd sure appreciate if you gave it a Favourite Point.