Artissima, the fair Artsy calls “Italy’s leading contemporary art fair,” is back for its 25th edition. Prepare to be wowed. Seven-hundred artists and 200 galleries are setting up shop in the Oval, an immense, 65,000-square-foot, former Olympic pavilion. Who will be featured? Everyone! The Main Section is devoted to different galleries, “Present Future” celebrates rising contemporary stars, and “Back to the Future” features already established pioneers. —E.C.