Built in the 1840's, Fort Knox was made to protect the towns and cities of the Penobscot River from British invasions.  It was meant to cut off passage to Maine's longest river and towns such as Bucksport and the booming lumber city of Bangor.  It is made of granite and has a pentagon layout.  It has many signs giving history along the way as you explore it's many long dark granite and brick hallways, defense trenches, granite spiral staicases, rooftop, cannon batteries, soldiers quarters, cannon ball hot shot ovens, gift shop, picnic area etc.  In the same park you will find Penobscot Narrows Bridge and Observatory towering above the fort, the tallest Bridge Observation deck in the world.  Come in October to make your way through the Fright At The Fort Haunted House or during summer for Bucksport Bay Festival and civil war encampment and reenactments.  Located where routes 1 and 174 meet in Prospect, Maine.

official site

http://fortknox.maineguide.com/