Here are a few suggestions for your next trip from Cologne(I)

In 2 hours, you can reach Milan, Verona.

In 3 hours, you can reach Turin, Bologna, Lugano, Padova.

In 4 hours, you can reach Genoa, Florence.

In 5 hours, you can reach Zürich, Rome, Luzern, Villach, Nova Gorica, Trieste, Thun.

In 6 hours, you can reach Genève, Lausanne, Koper, Bern, Winterthur, Innsbruck, Biel/Bienne, Jesenice, Klagenfurt am Wörthersee.

In 7 hours, you can reach Monaco, Schaan, Graz, Vaduz, Basel, Kranj.