Complex sentence: It grew up beside the Rheingrafenstein, a castle built in 1050 that was the seat of the count palatine of the Rhine, which was destroyed in 1689 by the French, but the ruins remain.
Split into simpler sentences: It grew up beside the Rheingrafenstein, a castle built in 1050 which was the seat of the count palatine of the Rhine. The castle was destroyed in 1689 by the French, but the ruins remain.