Code Vein: Outer Crossing Walkthrough

You will come to a place where you encounter Oliver Collins. Move here from your home base and talk to Shan, one of the NPCs. He sells gifts that you can give to your comrades at home base. You can buy them along with Old World materials. After the conversation, go down to unlock the shortcut. You will do this by lowering the ladder. After that, return to Shan and choose another path. There you will find Vivifer. Get down and go forward.  

Behind one of the turns you will find a dead soldier. Approach him and take the map of the Lair of the Dead. Go the other way. After going forward, you will find a lantern on the left side. This lantern marks the passage leading up. There you will find Mistle and discover the new Ruined City - Center region. Approach Mistle - this will trigger a cutscene.