Adventures in Middle-Earth: Rhovanion Region Guides - Rules of Play says:
The Rhovanion Region Guide is an invaluable resource for Adventures in Middle-earth further describing the lands of the River and the Forest – the rolling Vales of Anduin and the trackless forest of Mirkwood. It expands on the descriptions given in the core Guides, offering new sanctuaries and new perils for Player-heroes to discover.