COVE

This was a place near the river Rhine where Mary Shelly traveled along on her journey through Europe. Though she did not visit the castle, there are several points of connection between the novel she wrote and the place. The family in the novel Frankenstein bear the name of the castle, which is the most immediate point. The most interesting though is that decades prior, an alchemist by the name of Johann Konrad Dippel was born in the castle and would use it for dangerous experiments in his later years of life.

https://en.wikipedia.org/wiki/Frankenstein
https://en.wikipedia.org/wiki/Johann_Konrad_Dippel