I like to explore everywhere I can for treasure, armor sets, magic symbols, and better weapons, before continuing the main quest. Normally, you cannot enter Southrealm until the main quest takes you there. However, I found 2 ways to enter.
Apologies for thread necromancy; just wanted to add more to the topic.
There are a few more ways that I have found:
1. The first one is right by the Southrealm Border station itself. To the west are some mountains that, if you gain enough height, you can swing past the barrier. You can continue mountaineering until you reach the South Pass Fortress. From here, you can head south into the highlands and weave your way into Ostian.
2. I haven't personally tested this since I use Nehrim Expanded, but in vanilla Nehrim, you should be able to swim past the barrier if you head far east in the waters. In Nehrim Expanded, you can't do this, as a Sea Monster (slaughterfish) is placed at your location once you enter the cell and immediately kills you before revealing itself (the script actually hurts the player for 10k damage, ensuring that they will die. In base Nehrim, this fish is unused.
3. You can get there from the Tomb of the Treasury by wrapping around one mountain to steady yourself on another. This, of course, generally requires you to complete the side quest Traces to do this under normal circumstances if you don't have high speed and athletics. You could also reach the top of Collapsed Pass by heading west instead of east to shorten the journey (I haven't actually tested this, in particular, but I managed to get to the location from the mine. See below).
4. If your speed is at 100 or above via mods and your athletics skill is at least journeyman, you should be able to scale the barricaded path at the mine at Southrealm Collapsed Pass.
The Treomar route is not something I ever tried because it generally requires you to be further in the game to even really explore the area. Plus, you are kinda going out of your way to enter a high-level area in order to reach another high-level area when better alternatives exist.
Regarding the East Pass, there is an easier way to get up there. From the camp, head southwest until you see a rock with moss on the left side. Jump onto the corner of it, then gain enough height, continuing south while pressing Up (W) and right (D) on the keyboard. Once your character starts climbing inward toward the mountain for a bit, you should have enough clearance to scale the moss rock from your starting location. Head back northeast to the area you started from, from higher ground now. You should be able to reach the camp area from a higher vantage point. From here, you continue the mountaineering journey to the Southrealm.
If your destination is Ostian, the East Pass and the Border Station routes are generally the easiest routes to get there.
There are a few more ways that I have found:
1. The first one is right by the Southrealm Border station itself. To the west are some mountains that, if you gain enough height, you can swing past the barrier. You can continue mountaineering until you reach the South Pass Fortress. From here, you can head south into the highlands and weave your way into Ostian.
2. I haven't personally tested this since I use Nehrim Expanded, but in vanilla Nehrim, you should be able to swim past the barrier if you head far east in the waters. In Nehrim Expanded, you can't do this, as a Sea Monster (slaughterfish) is placed at your location once you enter the cell and immediately kills you before revealing itself (the script actually hurts the player for 10k damage, ensuring that they will die. In base Nehrim, this fish is unused.
3. You can get there from the Tomb of the Treasury by wrapping around one mountain to steady yourself on another. This, of course, generally requires you to complete the side quest Traces to do this under normal circumstances if you don't have high speed and athletics. You could also reach the top of Collapsed Pass by heading west instead of east to shorten the journey (I haven't actually tested this, in particular, but I managed to get to the location from the mine. See below).
4. If your speed is at 100 or above via mods and your athletics skill is at least journeyman, you should be able to scale the barricaded path at the mine at Southrealm Collapsed Pass.
The Treomar route is not something I ever tried because it generally requires you to be further in the game to even really explore the area. Plus, you are kinda going out of your way to enter a high-level area in order to reach another high-level area when better alternatives exist.
Regarding the East Pass, there is an easier way to get up there. From the camp, head southwest until you see a rock with moss on the left side. Jump onto the corner of it, then gain enough height, continuing south while pressing Up (W) and right (D) on the keyboard. Once your character starts climbing inward toward the mountain for a bit, you should have enough clearance to scale the moss rock from your starting location. Head back northeast to the area you started from, from higher ground now. You should be able to reach the camp area from a higher vantage point. From here, you continue the mountaineering journey to the Southrealm.
If your destination is Ostian, the East Pass and the Border Station routes are generally the easiest routes to get there.


