Road to Freedom

Road to Freedom is a Railroad main quest in Fallout 4.

Detailed walkthrough
There are multiple places to acquire the quest, specifically in Diamond City and Goodneighbor, from holotapes laying around, from overhearing conversations, or from NPCs who mention the Railroad in the course of the main story, such as Piper and Amari. When the objective to 'Follow the Freedom Trail' is added, proceed to Boston Common to find the beginning of the trail. Talking to the tour bot will provide additional information but is ultimately unnecessary.

Follow the distinctive red trail of bricks in the ground from location to location. The red line on the ground is largely unbroken but there are a few stretches that are obscured by debris. In these places the trail is "improvised" using trails of red paint across the street or along wreckage of buses and walls. The trail will take you past several Bostonian landmarks and historical sites, each with a "Freedom Trail" seal outside in the sidewalk, with a letter circled and a number added in red paint. The first seal ("7A") is at Boston Common right near the tour bot. The second seal ("4L") is in front of the Massachusetts State House. The third seal ("2A") is at the entrance to the Old Granary burying ground. The fourth seal ("6O") is near the entrance to Goodneighbor (the Old State House from pre-War Boston's perspective). The fifth seal ("3I") is in front of the Old Corner bookstore. The sixth seal (5R) is at Faneuil Hall. The seventh seal ("8D") can be found in front of the Paul Revere house. The eighth and final seal ("1R") can be found at the Old North Church, the end of the trail.
 * Alternatively, if players have already discovered it, they can simply travel to the Old North Church and skip the trail entirely.

Inside the Old North Church, kill a handful of ghouls and follow the lantern painting to find a way into the catacombs. At the end of the catacombs, there's another Freedom Trail marker with a ring that spins, similar in appearance to the eight seals on the trail. Rotate the outer wheel clockwise and counterpoise to align the letters with the arrow and press in the center to input the letter. Spell the word "RAILROAD" one letter at a time to open the secret door. If you make a mistake you must start spelling again from the beginning.

Once the door opens, go inside and the leader of the Railroad, Desdemona, shines a spotlight on you while two agents, Glory and Drummer Boy, train their guns on you. Speak however you want to them initially, it has no effect on your future relationship with them. Eventually Deacon will enter and list your major accomplishments in the Commonwealth, vouching for you. Desdemona will ask why you've come to the Railroad, if you know what a synth is, and most importantly, if you would risk your life to save them from their plight. Regardless of choices, the quest completes and Tradecraft starts immediately.

Behind the scenes
The Freedom Trail, including the red (both painted and brick) paths, as well as the embedded seals, exists in the real world as well.

Bugs

 * In some cases, the game will freeze when attempting to enter certain buildings in Boston Commons, including Old North Church, making this quest impossible to complete. The console command will teleport the player into Old North Church, past the entrance to the Railroad. The console command  must be used to go through and open the door to the Railroad properly. Exiting through the front entrance should work afterwards.
 * When first approaching the Railroad HQ, Desdemona and the other guards may instantly become hostile, making the quest impossible to complete, and making you enemies with the Railroad. They become hostile right after unlocking the door, making it impossible to start a conversation even if you approach slowly or use a Stealth Boy.

Gallery
Camino a la libertad Дорога к свободе