In preparation for the new survival mode, I have been trying to find a good overland route between the Castle and Star Light Drive in. But so far I have not really found a good path. That part of Boston seems to be stuffed with Mutants and Raiders. I tried heading through Bunker Hill and then down south, but that direction has non-stop engagements. I was hoping someone had a fairly simple route cutting through Boston. Even just connecting between Goodneighbor and the Castle would be great.
The safest route so far has to follow the rail road past Greygarden and Oberland station almost to Egret Tours. And then cut all the way across through Falons department store to Jamica plains and then up to the Castle. But it is long! BTW, following that route, but turn down the road after Oberland station will take you straight into Boston and Diamond City in no time. And with no real opposition.
To be honest, I kind of think a Hazmat suit or Aquaboy and just swimming from Bunker Hill to the Castle is the best method. But that means no power armor.