In case any New Yorkers are wondering, the party was held between Pell and Canal St, in a section of the subway that was created for the Second Ave Subway in the 70s, but will not be used in the one being built now (so, will likely never be used). And this is not confidential information:
If you remain on the downtown 6 train after the last stop (Brooklyn Bridge-City Hall), you get a glimpse of the abandoned City Hall station [1] as the train turns around. This was one of the very first NYC subway stations to open in 1904!
http://secondavenuesagas.com/2013/06/25/abandoned-sas-segmen...