To visit Fort Wolcott you have to do the first part of the "Peg Leg" side mission. The quest giver can be found at the harbor of the Homestead area. He wants you to find trinkets scattered around the Frontier, Boston, New York, and the Homestead. You can buy a map for these at any general store to make it easier. You only have to find 12 to be given the location to Fort Wolcott. Go to the Harbormaster and go to the Fort. This is the first part of Kidd's Treasure quest. Complete the fort and make sure you do the optional quests as well.