To find this Place in-game, use /where Siel's Western Fortress
Contains the entrance to the Left Wing Chamber.
If your faction owns the fort several NPCs will be available inside, including a Quartermaster that sells Morphing Recipes, and a Warehouse Manager. There will be a Teleporter NPC on top of the Outer Bailey.
All Lower Layer fortresses have a Postern Gate which, while heavily guarded, is the best way to enter and assault the fortress.
This fortress sells two unique categories of morph scrolls (other fortresses sell other unique morph method scrolls).
Morph method scrolls
Flux morphing scrolls for weapons, armor and accessories:
For details of flux levels see: Flux