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The Art Institute is the second-largest art museum in the country. Its collection of impressionist and post-impressionist paintings rivals those in France, and the number of surrealist works is tremendous. Download the free app for DIY audio tours; it offers several quick-hit jaunts, from highlights (including Georges Seurat's A Sunday Afternoon on the Island of La Grande Jatte and Edward Hopper's Nighthawks) to architecture and pop art tours. Allow two hours to browse the museum's must-sees; art buffs should allocate much longer.
The main entrance is on Michigan Ave, but you can also enter via the dazzling Modern Wing on Monroe St. Ask at the front desk about free talks and tours once you're inside. Note that the 3rd-floor contemporary sculpture terrace is always free. It has great city views and connects to Millennium Park via the mod, pedestrian-only Nichols Bridgeway.