John B.
Yelp
The hidden bar has (thankfully) been a long-obsolete necessity but speakeasy establishments seem to have become increasingly popular. Some are speakeasies more in name, given there's no real need for secrecy and deliberately hiding your bar is likely bad for business.
Captain Gregory's does a good job of merging the "hidden bar" vibe with availability. Originally paired with a Sugar Shack donut shop, the bar really has a hidden entrance behind a false wall. The namesake ship's captain from Maine is credited with inventing the modern donut, cutting a hole in a ring to better cook the insides than the previously-traditional diamond and long shapes of fried cakes and twisters. Sugar Shack has now been replaced with a paired sister restaurant: Railbird Kitchen.
As for the bar, Captain Gregory's offers top-end, craft cocktails. The menu regularly rotates and they keep it seasonal. When we went, we had a Pine Smoked Old Fashioned, Siren's Hymn, Jaws of the Python, and Royal Regatta.
Walk-ins are available on a first-come, first-served basis. Be aware that Captain Gregory's is a small, intimate space with deserved popularity and a reservation is required if you want to be certain you'll get in. They do charge for it, however, it also includes their namesake donuts.