The cheapest way to book Europe is not to buy the first cheap flight you see. It is to make the route and the budget agree before any booking becomes an anchor. A €35 flight can still be the expensive choice when it leaves from a remote airport, requires paid baggage, and adds a hotel night.
Start with two workable versions
Draft the trip twice: one version around the places you most want to see, and one around the easiest transport line. Compare total nights, intercity fares, airport transfers, and the cost of returning to your arrival city. This exposes whether an open-jaw flight—arriving in one city and leaving from another—saves enough backtracking to justify a higher airfare.
Shift each version by a few days. Midweek departures can help, but the larger saving may come from avoiding a festival weekend or moving one city out of a peak period. Compare the whole itinerary on the same dates rather than mixing the cheapest quote from different weeks.
Price door to door
For every flight or train, count the transfer to the terminal, baggage, reserved seats, food during the journey, and usable time lost. A four-hour train from city center to city center can be cheaper than a ninety-minute flight once the full travel day is counted.
Use one currency and keep a low and high figure for uncertain items. Separate international flights if the departure city is not fixed; otherwise a generic airfare assumption can distort the land route.
Book in order of risk
Once the route works, reserve items that are both important and likely to rise: long-distance transport, scarce lodging, and event tickets. Prefer flexibility when the refundable rate costs only a little more. Flexible hotels can protect the route while you confirm smaller decisions.
Do not prepay everything for the psychological comfort of being “done.” The goal is a low final cost with manageable risk, not the greatest possible number of non-refundable reservations.
The useful savings are structural
The biggest levers are usually fewer hotel changes, shoulder-season dates, well-connected bases, and avoiding repeated airport transfers. Small coupon savings matter less than removing an unnecessary travel day.
For direct answers, see What is the cheapest way to book a Europe trip? and How can I save money booking a Europe trip?. Timed-entry sites are a common early booking: check Eiffel Tower tickets and Colosseum tickets before you finalize each city’s schedule. When the route is ready, plan it as one priced itinerary before committing.