Yes, a Eurail Pass can be used on the S-Bahn (Stadtschnellbahn) networks in major German and Austrian cities, as these systems are typically operated by the national railway companies like Deutsche Bahn (DB) or ÖBB. In cities like Berlin, Munich, Frankfurt, and Vienna, the S-Bahn is considered part of the national rail infrastructure, and thus, a valid travel day on your Eurail Pass covers these trips. This is an excellent way to navigate from main train stations to city-center locations or suburban areas without buying extra tickets. However, it is critical to distinguish the S-Bahn from the U-Bahn (subway), trams, or local buses; Eurail passes are not valid on U-Bahn lines or most other municipal transit systems. If you use a "travel day" just for a short S-Bahn trip, it may not be the most cost-effective use of your pass unless you are also taking a long-distance train on the same day. Always ensure your pass is properly validated or active in the Rail Planner app before boarding to avoid fines during ticket inspections.