Open House New York (OHNY), allowing access to private and public buildings for architecturally and design enthusiasts.
Historically it runs on Columbus Day Weekend. This year I toured a LEED Certified apartment on 85th Street. The Lucida apartment we visited cost about $5,000,000 or about $1M per bedroom.
The Chrysler Building lobby, normally off limits, was open for the day too. Still heavily guarded, but at least tolerant to the art deco enthusiasts it attracted.