Here are a few suggestions for your next trip from Merten(Sieg)

In 2 hours, you can reach Köln, Düsseldorf, Frankfurt am Main, Liège, Essen, Dortmund.

In 3 hours, you can reach Brussels, Utrecht, Anderlecht, Eindhoven, Stuttgart, Schaerbeek, Nijmegen, Leuven, Molenbeek-Saint-Jean, Ixelles...

In 4 hours, you can reach Amsterdam, Rotterdam, Antwerpen, The Hague, Gent, Basel, Charleroi, Tilburg, Strasbourg, Brugge...