Burg Rheinfels, once the biggest castle on the Rhine was built in 1245 to protect the St. Goar tax collectors. It developed into one of the mightiest fortresses on the Rhine and withstood a siege of 28,000 French troops in 1692. But in 1797, the French destroyed it. The castle was used for ages as a quarry, and today the large ruins are only a fraction of its original size. Part of them have now been converted into a hotel.