Rivlyn appears to be a very important city in Kal Torlin in Before Shadowgate. It might even be yet another capital city like Stormhaven or Gwynenthel (or even alternate version of that city). On the map for Shadowgate (2014) there is a city known as Rivylyn between the Northern Arm and the Southern Arm mountains and on the western shore of the Wavenfaaver Source.