Purchasing tickets online — before you arrive at an attraction — not only means you’ll avoid long lines, it also guarantees that you’ll get in. In Florence, it's essential to reserve a scheduled entry to the Uffizi and Academia museums, while in Rome, an advance ticket lets you skip the line at the Vatican Museums. The same goes for the Sagrada Familia and the Joan Miró Foundation in Barcelona. If you don't want to navigate multiple websites, Viator.com and TickItaly.com can handle your bookings for multiple points of interest, but will add a hefty surcharge. Most major cities also offer a pass that gets you into museums and attractions (while letting you skip the ticket lines); some even include public transportation. Passes are a good deal if you're spending extra time in embarkation or debarkation ports.