In full disclosure The National Portrait Gallery is not exactly off the beaten path in Washington, DC.  But, I’m betting you don’t hear as much about the gallery as you do other museums in the city.  Case in point.  The National Portrait Gallery had 831,000 visits in 2017 while the National Air and Space Museum had 1.6 million visits.  (Smithsonian Visitor Statistics) So, yeah, in my book it’s a bit off the beaten path.