Lydia Mendelssohn Theater, University of Michigan, Ann Arbor

The Lydia Mendelssohn Theater, located in the League Building on the University of Michigan campus at 911 North University, is the gold standard for handicapped accessible theaters in my experience.  There is easy elevator access to the second floor entrance and not a single stair.  In addition, there are two multi-stall bathrooms near the entrance and a separate dedicated handicapped restroom, with toilet and sink in one small bathroom. What makes it even more impressive is that the building was constructed in 1929, demonstrating that it is possible to update an old building to be accessible without sacrificing character.

One small negative:  of the three entrances to the building, only the south entrance, on North University, is wheelchair accessible, while most of the available parking is closer to the north entrance. But that's a minor quibble in light of the ease of movement once you get inside.