The Sienna Forest is often considered the twin of the Egeria Forest in the same way that the Northern Celidon is the twin of the Western Celidon. This is not, however, entirely accurate. Unlike the Celidon forests, which are separated solely by the river Waelin, areas of grassland separate the Egeria and Sienna forests and they are not, in fact, part of the same overall forest. The Sienna lies directly east of the Egeria Forest, on the other side of the Eucrates River. To the southwest of it lies the forbidding Renfrewshire Swamp, and to the east is beautiful Lake Ildsam.