I would advise holding on to both keys in the set from the lockbox on the door that is street level. It was disappointing in the response time by the host. We unfortunately had taken one one key, you need both to unlock two different locks to the street level, information of which is Not in the description for the apartment. It was not great on our part on misplacing one key, but the response time was over 8 hours, with one guest being pregnant. Luckily, we got it resolved ourselves. I would advise, if you book here, you will be on your own. This is the first time I have come across this situation from Super hosts. What also was disappointing was the lack of care to see if the situation was resolved.
If it weren't for that disappointing experience, the place is awesome. It is in East Boston, a 2 minute walking distance to Piers Park, which you can see downtown and South Boston from across the harbor. It is about a ten minute walk to Maverick station, and the next stop to downtown, which is the Aquarium, which also takes you to the Boston Aquarium. That stop is also not too far from North End, which is the Italian district with 100s of Italian restaurants. The apartment is comfortable for up to 4 people and was fairly quiet at night. One room does have a closet which turns into a hallway which takes you to the emergency outside stairwell.