Many destinations, particularly in Europe, offer free downloads of maps, audio tours, and podcasts through official city government and tourism websites. Self-guided sightseeing tours of cities and major attractions, such as the Louvre, may also be available through Apple’s iTunes website. Some tours may require a small fee to download, but they’re usually less than $15.
The advantage of learning about the city before your arrival is that you can maximize your time by doing those things you really want to do, rather than trying to figure out your schedule while on the ground. Also, being oriented upon arrival just makes you feel more confident and excited about your adventure.