The Veneto in 5 days = Venice (2 days — there is no shortcut), Verona (Romeo, the Arena, the Adige), Padova (Giotto's Scrovegni Chapel — possibly the most important room in Western art), and Vicenza/Palladio (the architect who invented how buildings look). Plus Prosecco hills if you have a car.
Each day is a logical geographic loop. Mornings for sights, afternoons for food, evenings for aperitivo.
Days 1-2: Venice. Day 1: San Marco, Palazzo Ducale (Bridge of Sighs from inside), Rialto bridge + market, walk to Dorsoduro (Gallerie dell'Accademia, Peggy Guggenheim). Day 2: Murano (glass), Burano (lace + colored houses), Torcello (the oldest settlement — Santa Maria Assunta mosaics). Evening: cicchetti crawl in Cannaregio (away from San Marco). Day 3: Padova. Train 30 min. Cappella degli Scrovegni (Giotto frescoes — BOOK 2+ months ahead, 15 min timed entry). Basilica di Sant'Antonio. Prato della Valle (the largest piazza in Italy — 90,000m2). Caffe Pedrocchi (the cafe with no doors — open 24h since 1831). Day 4: Verona. Train 1h from Padova. Arena (the Roman amphitheatre — summer opera). Casa di Giulietta (the balcony — crowded, but you came to Verona). Piazza delle Erbe. Ponte Pietra + Teatro Romano. Day 5: Vicenza + Prosecco. Vicenza (30 min from Verona): Teatro Olimpico (Palladio — the oldest surviving indoor theatre in Europe, 1580). Basilica Palladiana. Villa Rotonda (4km south — the building that influenced every neoclassical building you have ever seen). Afternoon: Prosecco hills (Valdobbiadene, Asolo — UNESCO, tasting at a cantina).
Best time: April-June, September-October. Book skip-the-line tickets for major attractions.