To travel with an Interrail pass without paying extra for reservations, you must focus your itinerary on regional and local trains rather than high-speed or night trains. In 2026, most major high-speed lines—like the TGV in France, Frecciarossa in Italy, or AVE in Spain—require a mandatory seat reservation fee (typically €10–€20). To avoid these, use the Rail Planner app and toggle the filter to "No reservation needed." This will show you a network of slower, regional trains (like the Regional-Express in Germany or Regionale in Italy) that allow you to simply hop on and show your digital pass. While these journeys take longer and may require more transfers, they allow for total spontaneity and save you a significant amount of money. Note that some international routes, such as the Eurostar between London and Paris, cannot be done without a reservation, so you may need to book a few key legs in advance while keeping the rest of your trip "reservation-free."