The first time the downstairs unit in Carrie's apartment building has been seen. The only other time another unit was seen was in season four of Sex and the City, when Aidan purchases the other upstairs unit.
When Jackie and Carrie are discussing Carrie's noisy neighbours, Jackie mentions in has last apartment a woman was named 'The Wicked Witch of the West Side'. Carrie can clearly be seen wearing stocking like the wicked witch in the Wizard of Oz