Capitals absorb the search. The days that feel like travel are often a short line out. Sanssouci is forty minutes from Berlin and a park, not another dome. Zaanse Schans is twenty minutes from Amsterdam Centraal and still a working mill when the wind agrees. Óbidos is an hour north of Lisbon and a wall walk, not another miradouro. None of these need a new country on the itinerary. They need a morning that is not the old town loop you already did.
Further out, the same pattern holds with a longer train. The Three Sisters are two hours from Sydney Central and a stair into a valley, not a harbour extra. Kinkaku-ji is northern Kyoto, which is a different tempo from the station and Fushimi. The mistake is treating the capital as the whole map because the flight landed there. Aviasales will still show you the inbound fare; the regional ticket is a separate, cheaper decision you make after you land.
Pick one out-of-town morning per city. Do not collect three day-trips as a way of not choosing. The capital will still be there at dinner.