I have overactive bladder. In Downtown Crossing, I use the Macy’s bathroom - it is always clean and smells nice. If I’m around Copley Square, I use the bathrooms in the Boston Public Library. (There are also a bunch of smaller community libraries which have bathrooms.) If I’m in the Longwood area, I go into a hospital to find a bathroom. In the Government Center / Faneuil Hall area, during business hours, going into City Hall is a cleaner option than using the bathrooms at Faneuil Hall. (You will have to go through a metal detector.). Same for the State House in the area of Boston Common.

If I’m on the Red Line and need a bathroom, I’ll head to South Station, which has decent bathrooms. (So does North Station, but you have to walk through the arena area and they aren’t open late.) If I’m on the Orange Line, I normally head to Back Bay station, and use the bathroom there or go across the street to the fancy mall-type place there. I’ve gone to the airport on the Silver Line if I have an urgent need.

Stop & Shop and Home Depot always have bathrooms, though cleanliness can vary, especially at Stop & Shop.