After some fairly intensive research, I settled on 14 Union Park, and was not disappointed. The neighborhood felt safe even at night (and we walked and took the subways mostly - no car).
But the little enclave known as Union Park was just perfect. Read up on the history of this South End Boston square, and you'll know that it's a haven even within the larger neighborhood of the South End.
We were in the "Green Room" - 49 steps to the top, 4th floor... (We both independently started counting steps after climbing the 294 to the top of Boston's Bunker Hill Monument... wheww!).
But up there, we felt like we had our own personal world. With a nice view of the square below, and similar houses across the way. There are two bedrooms that share a bathroom down the hall. But the management has wisely decided that they'd only rent both rooms IF both parties are "together" - so you won't be sharing a bath with someone you don't know. So we took the Green Room, and the Taupe Room remained unoccupied. The bath has a very nice, glass-enclosed shower stall (could fit two - or even four if you're so inclined ;) and an old, cast-iron claw-foot tub. (I imagined how difficult it must of been for whoever carted that tub up those 49 steps...)
What I don't think I realized when I booked was the little "kitchenette" that is part of this deal- small fridge - stove-top -sink - supplies such as paper plates and bowls and utensils included. That was great.
In fact, I'm somewhat ashamed to admit, that we felt sooo "at home" that we didn't even bother to to close, let alone lock, the bedroom door. So that last morning when we were lounging around but also getting ready to leave, I guess our TV was echoing out the door and down those 49 steps...someone on the floor below asked us to turn it down. Ooops! But I only relate that to let you know how comfortable we felt there - like we had our own little slice of Boston Cream Heaven.
I don't know what the other rooms are like, but I don't think they have that kitchenette...
And people like us are maybe being too noisy above there heads, so top floor for me.
And there's this other feature...When we got there that first rainy night...we opened a door right between the Green Room and the Taupe Room.... We called it the "Spooky Stairs" lol Old, unpainted wood stairs leading up into a darkness we couldn't penetrate. What's up there? You'll probably never discover because the management will most likely put a deadbolt on it after reading this ;) But it added to the charm and the realization that we were staying in a significant piece of Bostonian history.