How often do we get a chance to see acrobats like Toronto's High Strung Aerial Dance company float gracefully above us in the shadow of tall buildings? Or be confronted by a sideshow spectacle from another era, like Thom Sellectomy swallowing two-foot swords and five-foot balloons? Last year when producer John Mills and the New East Side Association proposed a four-day festival of sidewalk entertainment, audiences anticipated little more than another street fair--certainly not a pocket-size carnival. Besides High Strung and Sellectomy, this year's fest features traditional outdoor amusements such as magicians and veteran folkie Steve Rich along with novelties such as the University of Hip-Hop ensemble, contortionist Yogi Laser, mask and puppet artists, and the Handsome Little Devils, jugglers whose specialty is dueling--on unicycles. The festival takes place at Illinois Center Plaza, located east of Michigan on Stetson between Wacker and Lake; at Prudential Plaza, 180 N. Stetson; and at various sites along Michigan, Randolph, the lakefront, and the river. It runs from 11:30 AM to 3 PM Thursday, July 31, and noon to 8 PM Friday and Saturday, August 1 and 2. Admission is free, though donations to performers are encouraged. For information check the association's Web site, www.chicagoneweastside.com.