This quest is a prerequisite to completing the second-to-last main story quest, The Molecular Level and is triggered when you start the Unlikely Valentine quest earlier in the main story. Road to Freedom will take you to the famous tourist spot known as The Freedom Trail. The waypoint indicator will lead you to Boston Common, near Park Street Station. Look for a fountain with a board that reads, "At Journey's End Follow Freedom's Lantern."
Notice the circular marker on the ground and the skinny red brick path nearby. The red bricks will lead you to your destination. More than 200 years of rubble will obscure some sections of the path. Every time the path ends, look in every direction for the next section of the path. This is route is meant to point out historical buildings, so you'll find the red path near many of the older 18th century structures (plus one graveyard) in the immediate area.
If you follow the route correctly, you'll come across the following landmarks in this order:
Massachusetts State House
Old Granary Burying Ground
Old State House
Old Corner Bookstore
Paul Revere's House
Old North Church
Every landmark also has a circular marker on the ground. If you manage to skip any of these (which can happen), you don't have to backtrack. Just continue your walk to Old North Church. Expect a lot of Mutants along with way.
When you've entered the church, take care of the Ghouls, then make a U-turn to the doorway at the opposite side of the church. This will take you to the church catacombs. Remember that you can use your Pip-Boy to light the way.
Follow the lantern markings on the ground until you reach a metal dial on the wall that reads, "FREEDOM TRAIL RING." By looking at the edges of the ring, you can turn the dial clockwise or counterclockwise. Spell "RAILROAD" by aligning each letter at the 12:00 position and pressing down on the center of the ring each time. A door will open once you've entered the letter D.
The Railroad faction are apprehensive of strangers, especially those who manage to find their hideout. You can win them over with socially graceful replies and by describing your backstory in detail. This encounter will complete the quest. If you're taking on this quest to complete The Molecular Level story quest, the next step is show them the Courser Chip.