Ruins are always worth a visit! It's on the path, so it's not a special detour. The ruins are not particularly large. At the top there is a small viewing area with a bench. Beautiful view of the Danube included.
Eckartsau Castle is located just 24 kilometers from the Vienna city limits, directly on the Danube cycle path and in the middle of the national park. Hidden in a natural idyll, but still easily accessible!