You’re probably already aware of Sixth-and-a-Half Avenue (6½ Avenue) in Midtown, a great Daily What?! in itself. 6½ Avenue takes you through privately-owned public walkways within buildings, mid-block from 51st Street to 57th Street. But not too far away, in the Diamond District on 47th Street is another mid-block arcade, the Plaza Arcade, featuring almost predominantly gold shops. The passageway has one entrance on the ground floor of of 27 W 47th Street, between 5th and 6th Avenue, and amother at 32 W 48th Street.
In this Google satellite view, you can see how the buildings connect, unlike the surrounding buildings:
Companies inside include Ross Metals and Harold Gold, Inc.:
One of the entrance/exists of the passageway on 47th Street:
Also check out the Gold ATM, located in Midtown as well!