Endless routes are possible :D

Naples - Rome - Florence - Venice - Trieste - Ljubljana - Zagreb - Budapest - Vienna/Bratislava - Prague - Dresden - Berlin - Cologne - Amsterdam - Brussels - London - Paris - Strassbourg - Colmar - Switzerland - Milan - Genoa - Cinque Terre - Naples this is a City Route maybe mix Cities with nature spots.

is just one example

You may start makeing a list of Cities/Places you wanna explore and then check the traveltimes.

Route Suggestions by Interrail

Reservation Free Route ideas

Thank you so much!