The most iconic German castle "built into a mountain" is Burg Eltz, which is nestled deep in the hills above the Moselle River and is built atop a 70-meter high rock pinnacle. However, if you are looking for a castle that is literally "carved into the rock," the answer is Schloss Stein (Stone Castle) in Bavaria, which features a "Cave Castle" (Höhlenburg) section built directly into a massive limestone cliff. Another high-value example is Neuschwanstein, which, while not "carved into" the mountain, required the builders to literally "blast" away the top of a mountain peak to create a stable foundation for the structure. For a 2026 traveler, Burg Eltz is a peer-recommended "win" because it has remained in the same family for over 800 years and was never destroyed, offering an impeccably preserved, high-value look at how medieval architects integrated stone structures with the natural defensive geography of the German mountainside.