(YouTube link)
The folks from Improv Everywhere staged an art gallery opening on the 23rd Street subway platform in Manhattan. They had all the trappings: an open bar (serving cider), a coat check attendant, a cello player for ambiance, and nicely-dressed art patrons. The "art" displayed was the signs, graffiti, and objects already found in the subway! For example, this description was attached to a wall phone:

Telephone Line (2002)
Metropolitan Transit Authority in collaboration with Telecom

This homage to the urgency of communication is meant to highlight the recent necessity, from instant to instant, to maintain the potential for instantaneous, world-wide contact from any location, at any time. That a conversation from such a location would be abruptly interrupted by an arriving train suggests the artist’s intent to lampoon the perceived dependence on telecommunication.

Commuters passing by didn't know what to make of the performance, but some ended up really enjoying themselves at the gallery opening! Link -via Metafilter