A hotel in the Seaport District in Boston, MA next to the BCEC, the new Boston convention center. Boskone moved there in 2007 for Boskone 44 and has remained there since. Arisia followed in 2012.
The hotel is blessed with large amounts of excellent function space and plenty of sleeping rooms, but cursed with a location that is still remote (at least a few blocks) from most restaurants and other amenities, including public transportation.
Nonetheless, it is currently in a sweet spot in Boston, having the best overall balance of location, suitability as a convention facility, affordability, and availability. (I.e., it's in downtown Boston, but its location is sufficiently awkward that it's not yet priced out of fannish reach.)