Great Southern Lake
The Great Southern Lake, also known as the Southern Lake was a lake that was included on maps in Blood Omen and Blood Omen 2. It was a playable Location in Soul Reaver 2 .
The Lake was shown in the main map of Blood Omen although it is inaccessible in that game. Blood Omen 2 also featured a map of it in Kain's 'dream' sequence in the opening video.
In Soul Reaver 2, Raziel exited the Sarafan Stronghold to find that it's Northern balcony overlooked the Southern Lake. Raziel was able to escape the Stronghold from this ledge, but was not able to re-enter as the ledge was too high. The Lake itself was fed by many waterfalls and seemed to have a healthy amount of fish swimming in its waters. At the bottom of the lake was a set of ruins.
Light Forge and Sarafan Stronghold in cliffs around the Lake
When Raziel returned after gaining the Dark Reaver , he was able enter the Light forge , in the cliff face on the banks of the Lake and gain the Light Reaver . He was then able to use the Light Reaver to activate the Light Crystal and re-enter the Stronghold through it's large submerged doors.
Further on in Soul Reaver 2, when he reached the Sarafan era. Raziel was to exit and re-enter the stronghold again, it was covered with a thick layer of ice, which Raziel had to break using the Fire Reaver before he could re-enter the Stronghold.
Notes
The ruins of Soul Reaver 2's Spirit Forge at the bottom of the Southern Lake
The ruins at the bottom the lake are believed to be the remains of the Spirit Forge removed from Soul Reaver 2 - Both the Soul Spiral (The symbol for the deleted Spirit Glyph from Soul Reaver) and the Spirit symbol are featured upon it's ruins.
In Blood Omen era maps, much like the Lake of Tears , there are sea serpent symbols in The Southern Lake. These may also have similar origin considering that both The Light and Spirit Forges were in the Lakes vicinity.
The Lake also had many streams and rivers flowing into it, it is likely that the stream Raziel followed in Defiance and the river seen flowing underneath the Stronghold in Kain's Defiance visit were part of Lakes tributaries. Blood Omen 2 maps appear to show the Lake flowing into the Great Southern Sea