WORD OF ADVICE: keep an eye out for Deathclaws. Those motherfuckers can be stealthy as. Point: recently, I decided to go and explore Haymarket Hall, while deviating from the Freedom Trail (I've already joined the Railroad, but decided to follow the Trail in it's entirety for once). So yes, after clearing out the Raiders and the Protectrons, I reached the Garden Terrace (a marked location, yes).
Just when I thought I was safe; BOOM. A motherfucking ALPHA DEATHCLAW appears out of nowhere, and proceeds to rip level 16 Chris Arlington (me) and Deacon apart. How I managed to escape back inside without being absolutely slaughtered, I may never know. Was it Luck, or did my Martyr's Chest Piece (slows down time temporarily when your health goes below 20%) save me?
Yeah, it was probably the chestpiece. Good thing I found that, right?