On Dathomir you’ll have to head back to the temple so leave the ship and head for tall door out of the opening area. Now you have the climbing claws you should be able to take the path on the left which will take you straight to it.
Go through the big doors, fight your way through the room and go out to the area with a double rope swing, Meditation Spot and the stairs up to another big door. Go through there and you’ll reach the bridge to the temple where you met creepy cloak guy.
Go into the temple and activate the wall at the end to trigger a cutscene that concludes with a short fight. Once that’s done the door will open and you’ll be able to proceed into the temple proper. There’s a few Night Brothers to kill in there and when they’re gone use the orange Climbable Wall to reach the area above where a beam will take you over to the other side and a Force Echo.
Once you’re done, head into the temple via the tiny gap at the end of the room where you’ll meet the Night Sister for a chat. Once you’ve finished talking you you’ll see Taron Malicos (creepy cloak dude) waiting up ahead for a boss fight.
Once Malicos is dead you’ll talk to the Night Sister again and then be able to take the platforms behind her to reach the final part of the temple and pick up the Astrium.
Once you’ve got it, it’s time to head back to the ship and go back to Bogano and open up the Ancient Vault you went to visit right at the start of the game.
Once you reach Bogano, go to the Ancient Vault and use the Astrium to open it. You’ll reveal a black, mirror like wall you can interact with that will trigger a playable cutscene vision. When that’s done you'll have to fight the Second Sister in another unwinnable fight, so just inflict damage until you trigger a cutscene. When she's gone you’ll activate a final location, the Fortress Inquisitorius, and be able to finish the story. The game world will still be playable and explorable afterwards, so don’t worry about tying up loose ends first - just head back to your ship, set course for the Fortress and get it done.
The Fortress is a small self contained area you won’t be able to revisit once it’s done and it’s basically a series of kill tunnels where you murder all the opposition until the credits roll. Just head to the smaller building on the left once you start in the water, and then fight your way to a generator you’ll need to start by Force Pulling the cable to it and then pressing the button. That will cause an explosion and create a new path on the left when you leave the room.
On the other side of the door you’ll find a red pipe you you can’t cross because it’s on fire. Look right and the window should light up blue indicating you can Force Push or Force Pull it to break it open and flood the tunnel. When you’ve done that, swim out of the broken window and keep going until you surface in an area with a Meditation Spot.
Head through the red tinged door into the Inner Fortress where you’ll fight some scout troopers and heavy assault troopers. When everyone’s dead head up the stairs where you can trigger some switches to remove some of the floors in the room you’re looking into where you can see some Purge Troopers training. Once that’s done in go into the room via the door below you and fight several waves of just about every Imperial enemy you’ve met in the game.
Once that’s done, you'll be able to use a Meditation Spot and then slice the door at the back to get into the Prison Block area.
There’ll be a Purge Trooper in the Prison Black and a ton of standard troopers, so equip your double bladed saber and prepare for a lot of blaster defelections. When everyone is dead head to the middle level and look for the one window that isn’t red and go to it and activate the switch. You’ll meet Cere and then be able to go through the large doors on the lower level into the Fortress Citadel.
Use the switch on the right to access the bridge and then use the Meditation Spot at the end before proceeding into the final boss battles of the game - go into the interrogation room and interact with the switch in front of the chair to set the final part of the story in motion.
Once everything has played out you'll find yourself back on the Mantis and able to explore anywhere you haven't 100% complete.
