People come up here for the museums and walk straight past the galleries, which is a shame, because the galleries are free and you can be in and out of one in six minutes.
The Upper East Side gallery scene isn't Chelsea. There are no freight elevators and no crowds on a Thursday night. It's mostly townhouses and upper floors of prewar buildings between 64th and 79th, on Madison or a few doors east and west of it, showing blue-chip twentieth-century work and secondary-market pieces you won't see anywhere else. Nobody will bother you when you walk in. Sign the book if there's a book, look, leave.
A few things worth knowing before you go. Most galleries up here run Tuesday to Saturday and close on Mondays, and a lot of them also close on Saturdays in high summer or keep appointment-only hours in August. September is when the season restarts and the new shows go up, which makes early fall the single best time to do this walk. And the buildings can be quiet enough that you'll think you've got the wrong address. Push the door anyway.
Here's the route we'd walk, south to north, starting from East 62nd Street.