This achievement is unmissable and part of the main story.It is apparently possible to skip almost this entire part, as I describe in the spoiler below.
*** Spoiler - click to reveal ***
You can get through the talking door regardless of how many star stones you have by dropping one of your pyramids and moving it through the door with telekinesis, then teleporting to it. You can also apparently skip the first two trials and just light the candles as described in the spoiler towards the end of this guide.
The difficulty ramps up a lot in the end game and it has the potential to be enormously frustrating. I'm going to include a number of links to the resources I used to figure out how to get through it along with some commentary that I hope is helpful.
Once you enter the Source Temple you'll quickly learn the shortcut you were promised isn't going to work out for you. There will be no combat for this entire section, but there are a number of situations where having high perception (I buffed mine to 14 to be safe, but from what I understand, 9 will be enough-if anyone can confirm, that would be great). You will potentially be hit by poison and fire damage unexpectedly, so this would be a good time to swap to gear with perception, health, +Con and fire/poison resists.
The puzzle will also require you to navigate through areas blocked off by bars or grates. This can be achieved by throwing a teleportation pyramid through (aided by telekinesis), but a scoundrel with Cloak and Dagger or an Aerothurge with Teleport will make it a lot easier.
You'll also need to have located a total of 12 star and blood stones (our of 17 in the game). I kept all the inert stones over the course of the game as well as blood stones and had 9 inert stones (activated star and used blood stones) and 3 unused bloodstones. You shouldn't need to have the inert stones, they're just a count of how many areas you've unlocked in the Homestead. If you haven't unlocked all of them (the Temple is the last), you can use unused bloodstones to activate more rooms. If you still don't have enough, below is a list of locations put together by the Wikia that shows where you can find them. There is supposedly one in the entrance area, but I wasn't able to find it, even with high perception.
http://divinity.wikia.com/wiki/Blood_/_Star_Stone_LocationsIf you're unsure, continue through the temple entrance to the path that will be revealed on your map but is blocked off by rocks. Find a switch near the rocks to remove them and continue on. You'll come to a door that will either confirm that your memories are complete (you've unlocked enough of the Homestead) or that you're not yet whole and need to find/use more stones.
The actual puzzles that form the Trial of Ascension are quite difficult. You get some guidance from the developers in the form of a few books found in the library at the far end of the level, but they're pretty obscure. I'll put hints to the three most frustrating parts in spoilers below, but for a complete walkthrough, Youtube user Watchwithwaddy (
https://www.youtube.com/channel/UCHEokFJkMX8eB8XIS8CQl-Q) did a great job going through the whole thing. I've linked his video below.
First Test:
*** Spoiler - click to reveal *** The first part of the puzzle requires you to step on the pressure plate in front of the giant head to open the locked door to your immediate right. The pressure plate in the next room opens another locked door to your immediate left. Stepping on the pressure plate in this room triggers poison gas (can be shut off with the idol at the far right of the room as you enter. Exit the room by finding and pressing a button on the far wall. Past this area is a broken bridge to the right. Cross with bridge with pyramid tossing or teleportation of some kind. The trick here is that you need to break down the door blocked by stones to uncover a new warp waypoint. You can now warp directly to the treasure room and complete the first test (see the books for hints).
Second Test:
*** Spoiler - click to reveal *** From the treasure room, pyramid toss or teleport through the grate to access the mirror which brings you to the earth door key. With perception, you can find a button on the wall to unlock this door, otherwise warp to the main chamber waypoint. Navigate through the earth door (behind the room you mirrored into) until you find the air key.
The air door is past the first door you entered (under this guide, to the immediate right of the giant head). The second locked door is opened by the pressure plate in the poison room. Follow the hallway until you find a hatch.
The hatches will basically take you in a circle around a series of rooms (some of which contain lava and others poison cloud traps, though only the poison damage can hit you if you don't move until you know where you're standing). There are several chests that can be unlocked with keys found in the rooms, but to proceed with the test you'll need to keep jumping through the area until you reach a room with a hatch connected with a grated off door to another room with a hatch. Pyramid toss or teleport your way into this next room. Have high perception (I had 14, but have heard you need at least 9) to locate a button in this room. Press the button to open a hidden door to a room you can't access any other way and use the hatch to jump to the next part of the test.
Third Test:
This really isn't too bad and the solution is explained in the books found in the library, but details are in the spoiler below.
*** Spoiler - click to reveal *** Go to the far end of the temple. Light all the candles in the outer circle, then back off (I had to walk around a bit) until the candle area flashes. Then light just the center candle and again back off until there is a flash. Finally, light the three candles (two on the outer ring and the center candle) that point directly at the bookshelf on the wall furthest from the entrance. Another flash and the bookshelf will slide away to reveal a passageway. Achievement pops shortly after entering the passage
Watchwithwaddy's Youtube guide.