In Order to get the void chapter for the base game you will need to have 3 requirements

-No Flashlight at ALL, dont even pick it up.

-Less Than 6 Deaths

-Under 90 Minute's

after those requirements are met in chapter 3 after you get the key card and open the door, then ride the ferry and crossover to land and traverse up the steps to the coliseum looking structure, there should be a red anomalous looking sphere, you will also get a audio quip of "what is that thing?" enter it then find the Shepard of the Void, he will be near where you spawn holding a lantern, follow him until he stops at a rock overhang near a lake. go towards the lake and a cut scene will appear. ill leave the cut scene for you to see.

The Summoning - DLC

Chapter 5 Requirements

none.

in order to get chapter 5 you will need to be in chapter 4 the summoning, head towards the huge watchtower that is on the path to the right when you spawn in, get to the foot of the watchtower then look around on the hill opposite the amusement park fence, there should be a little hole there for you to find.

the rest is super amazing to witness so i will let you bask in the glory of it.

thanks for reading my guide, sorry it wasn't the most professional, i will be making more guides soon though so keep a watch! and this is coming from a person with 26 hours