Rick's essential Prague orientation walk (audio ~75 minutes). It runs from Wenceslas Square (the broad boulevard where the 1989 Velvet Revolution played out), through the old town to the Old Town Square with its Astronomical Clock, the Jan Hus memorial, and the Týn Church, and on down to the Charles Bridge, threading the city's history as it goes.
A great first-afternoon activity, and it covers the ground we're staying right next to. Free from Rick Steves Audio Europe; the route map (PDF) is on this page.