For the location from Diablo Immortal, see The Terminus (Diablo Immortal).
The Terminus is a small zone found just past The Archives of Zoltun Kulle in Act II of Diablo III.
From there, player(s) can travel to The Storm Halls and The Unknown Depths, where the Shadow Locks needs to be open to get access to the Realm of Shadow.
After recovering Zoltun Kulle's body from the Realm of Shadow, the way to the Soulstone Chamber is finally open.
A Waypoint is also located here.