Ringwil
From Tolkien Gateway
The river Ringwil was a river of Beleriand. It began in the hills about Nargothrond, and flowed north of the hidden city until it met the Narog. Where it met the Narog a secret door was built, which was used by Lúthien to escape from Nargothrond when Celegorm and Curufin held her prisoner.
