Path of Exile

For me, this achievement was somewhat luck-based. While I could have got lucky with @Frankies Back solution, I believe the achievement popped for a different reason. I believe the third Treasure Key is related to the Mysterious Darkshrines hidden throughout the Labyrinth.

The rest of the guide is correct as far as locating the Darkshrines, there is substantially more detail on additional key drops located at the poelab.com site, all credit goes to them. Specifically here: http://www.poelab.com/?page_id=493#Izaro1

Each phase of Izaro has a chance at getting an extra key. Use the above link and the additional challenge to reward yourself with an extra key. If you get one from a Darkshrine, then you only need to complete one additional challenge to get the achievement.


Original article:

My basis is from the wiki article here: https://pathofexile.gamepedia.com/Mysterious_Darkshrine

First question, how do I find these secret shrines?
In all my runs (and there were quite a few), I only was able to find the shrines on the following areas:

* Estate Path
* Estate Walkways
* Mansion Path

After several hours running the labyrinth, I ended up skipping through all other maps. Every single time I played those ones above, I would always find a shrine hidden somewhere.

So you're on the right map, how do you find the shrine?
The shrines are in a hidden area of the Labyrinth. You can see the hidden area on your map - it looks like a small room with no doorway. The switch is just outside, but doesnt show up on the map like your usual switch (green icon). You can see on my minimap here, the hidden room to the north-east of where I'm standing:


Once you flick the switch, part of the wall will move for you to go in. Inside you'll find a handful of rare/magic enemies to kill... and the shrine.

The shrine speaks some cryptic message and often leaves you wondering what just happened. First of all (confirmed on the wiki link above), all shrine effects are beneficial in some way, so by all means use it. If you bring up the full-screen map, you can see in the top-right corner what benefits you have in the map. If this is your second or third shrine, I recommend checking what benefits you have BEFORE you use the shrine so you can see whats new.

The most common effects for me were...

* A random shrine effect - only one effect can be in effect at once, so if you get this result a second time, the first effect is overwritten. I believe a patch coming out soon is going to fix this. You'll have a big fat icon appear above your head when this happens.
* Reduced trap damage in the labyrinth - this is nice, but not what we want for the achievement.
* Traps are disabled in the final encounter - if you're running this on Normal, there are no traps anyway, so this is kinda pointless.

All these 3 above effects are displayed on the full-screen map. If there is no additional effect displayed, that means you've picked up one of the following rarer effects:

* Izaro is guaranteed to drop one unique - this is also nice, but not what we want right now.
* You get one extra use of the Divine Font - for me this was a bit of a waste too.
* Izaro drops one extra Treasure Key - this is the one we want.

I say again, these will not appear on your full screen map. If you use a shrine and nothing happens, you have got yourself one of the above effects.

This is the point where you cross your fingers and kill Izaro. The achievement unlocks as soon as you kill him.

Update: http://poelab.com does the layout for the labyrinth for the day,, including which areas have a Dark Shrine for you to seek out.