'Map of Siofra River and environs. Two great rivers flow beneath the Lands Between, the Siofra and the Ainsel. This vast region is said to be the grave of civilizations that flourished before the Erdtree.' The Siofra and the Ainsel are the canon's geological proof that the Lands Between is a layered place : underneath the visible Limgrave-Liurnia-Caelid-Mountaintops topology lies an entire second world of buried rivers, dead cities, and forgotten gods. The Siofra, accessed via a hidden well in eastern Limgrave, opens into the Ancestor-hunters' moonlit forests around Nokron. The Ainsel, accessed via a different well in Liurnia, descends to Nokstella and the Lake of Rot. Both rivers eventually meet at the Deeproot Depths, where the Erdtree's roots end.

'Map of Deeproot Depths and environs. At the very depths of the Erdtree's majestic roots lies the source of the Ainsel and the Siofra rivers. Here too begins the network of Greattree roots that spread far and wide.' Why the Erdtree did not extend its order to the underground is the canon's quiet answer to where the buried civilizations went. The Erdtree's roots stop at Deeproot Depths because the Eternal Cities, Nokron and Nokstella, refused to let the gold pass them. The Underground Rivers are graveyards of pre-Erdtree religions : the Regal Ancestor Spirit's hunters, the Eternal City's sorcerers, the Tibia Mariners' boatmen. The Tarnished's descent into Siofra and Ainsel is the canon's clearest archeological pilgrimage : every chamber down is a chapter farther back in time.