Easiest access is through the Divi Little Bay Resort. To get to cache - Take the good road through the resort, then climb the rocky path up to the fort. Fort is about 5 minutes uphill from the SeaBreeze Cafe, which sells water for the way up and drinks to celebrate when you get down.
Uphill climb is steep to a Florida girl (flat-lander), but my Canadian father-in-law did it and said "NBD", which means 'no big deal'.
Thanks to "DIVISXM", General Manager at Divi Little Bay Resort, for being this cache's local guardian.
Small note on cache maintenance: As noted above, there is a local cache guardian. Name and contact info on file with geocaching.com.