In this guide, you will learn where the Freedom Trail is and how to follow it to the Railroad in Fallout 4.
Most of the city has disappeared, but there are several major landmarks that remain; one of them includes the Freedom Trail. There is a quest involved with it, and at the end you will find the Railroad. This is a shadowy organization dedicated to saying Synths from the prejudices of society.
How to Follow the Freedom Trail

You can find the Freedom Trail in downtown Boston, which is located to the east of Diamond City. The quest can be started randomly by listening in on a couple of Diamond City residents near the “Bounties” board, or by continuing in the main quest line until you are tasked with finding the Railroad.
The Freedom Trail itself starts at Boston Commons — a small park which you can find inside the ruins of the city. The first plaque is located near the fountain, with the help of a nearby tour guide, you can activate it.

Next to the plaque on the ground, you will witness a red line running along the sidewalk. This is the way of the Freedom Trail. You will have to follow it to continue along its path when debris covers it, in order to reach the final destination.
There are multiple plaques scattered throughout the Freedom Trail. They all have a separate number and letter written and highlighted on it, which you might want to mark for use later.

The last spot is the Old North Chuch. Now, you will have to clear the place of some Feral Ghouls, then head toward the basement, which you will find to the back right upon entering the church.
At the end of some long hallways, you will see another plaque with a door it’s nearby. This is the place where you will witness those highlighted letters come into play. If you took notes you should have 7-A, 4-L, 2-A, 6-O, 3-I, 5-R, 8-D, and 1-R. It must be easy to figure out, but if you failed and need the answer it is spelling out Railroad.

Now, you will have to put your cursor on the outer ring to rotate it so that the inner ring points to different letters. Make sure to Spell the right word by activating these in the correct order and the door should open. Now, you will meet another of Fallout 4’s main factions, the Railroad.
Fallout 4 is an open-world action RPG developed by Bethesda Softworks and released worldwide in 2015 for PC, Xbox One, and PlayStation 4.