Hi Marcus,

The answer to your question has to be: in general yes, but it depends.

If you could let us know roughly which countries you’re planning on travelling through, we can answer your question more fully.

There’s a world of difference between France on the one hand (where almost all long-distance trains require reservation and there’s only a small allocation of places for Interrail passholders) and Czechia, for instance, on the other (where most trains are very frequent and reservation is almost always* optional).

If the distances you’re trying to cover per travel day aren’t too great, and you don’t mind taking the slow route, you can cover the same ground on reservation-free regional trains in most cases, so it’s rare you’ll be completely stuck if reservations for a particular fast service sell out.

The country I would most strongly red flag for more spontaneous travels is Spain, because almost every train has to be reserved at significant expense, and some major cities only see direct service once or twice per day.

*except Supercity Pendolinos east of Prague.

Sure you can. For many trains, a reservation is not required so you can even decide on the spot.

But there's no general rule and there are big differences between countries and operators.

Depending on the country and trains, your options may be limited if the train(s) you would like to use are full or full for pass holders. Long-distance trains in e.g. Italy, France and Spain have mandatory reservations. In Italy and Spain, there are no quota for pass holders in domestic trains but trains can get full (although booking a few days in advance will often be enough). In France, there is a limited pass holder quota for 10 EUR reservations and if that is full, then the price goes up to 20 EUR until the train is full.

International long-distance trains from/to France, Spain and (partially) Italy do have limited quota for pass holders and reservations are more expensive and often only available on paper. So if a train is full for pass holders, you'll have to be flexible, e.g. use another train with available seats, find a reservation-free alternative or go somewhere else. You can of course also buy a normal ticket but that can be much more expensive.

Ah-the good old days when you could more or less board any train-also overnight-and just sit with heaps of ditto young people in the gangway and have a lot of fun. No fancy&expensive Hi-Speed then-hours delay and no compensation and no water.

The point is-as above also points out-its quite often very well possible to use only RES-free trains, this will of course take longer and mean more changes. But the modern travelplanners also seem to send all people without any knowledge of trainsystems but only relying on their holy fone in those fast trains.

To complete overview: ALL Long-distance trains must also all be reserved in PL=POland (PKP), SE=Sweden (SJ and others) NO=NOrway (Vy and others), FI=Finland,VR, RO=Romania (CFR-also there NOT valid on about all other local trains) and GR=Greece (TrainOSE), and TR=Turkey, TCDD-but hardly any trains running there at the mo.