This space is more like a contemporary art museum than the scores of galleries it has helped draw to the neighborhood. Besides installations by diverse artists on its four floors of space, you might find an exhibit from Dia's permanent collection, which includes creations by Joseph Beuys, Walter De Maria, Dan Flavin, Blinky Palermo, Cy Twombly, Richard Serra, and Andy Warhol. Don't miss a visit to the roof, which has a two-way glass pavilion designed by Dan Graham that invites contemplation of the surrounding cityscape. A vibrant bookstore designed by Cuban artist Jorge Pardo has one of the city's best art selections. COST: $6. Subway: C, E to 23rd St.