Complex sentence: The setting started out as a hotel, but narrowed down into a hotel bar, and then changed into a "neighborhood bar" because "the interior (of the actual Boston bar) is brick, polished mahogany, and brass".
Split into simpler sentences: The setting started out as a hotel but narrowed down into a hotel bar. Then it evolved into "Boston neighborhood bar" because "the interior (of the actual Boston bar) is brick, polished mahogany, and brass".