All Credits go to K1llerM0nkey from Trueachievements.com!For this achievement you need to enter the 3 treasure chamber Portals, due to the way im making these videos they will all be seprate.
1. For the first Treasure Chamber after you kill the first boss (First Warden) you want to make you way back towards the the start of the level, goto near where you got the key, and head left instead and you should see the first portal.
2. For the second Treasure Chamber after you kill the boss Infiltrator you want to make your way back if you look at yekta go up the stairs to the right to see the portal.
3. For the third and final Treasure Chamber after you kill the Annihilator you want to head back the way you come, in the next room (if not cleared) you will see that weird dog like tree looking thing :> head down the stairs ahead of you(or drop off) when your at the bottom the last treasure chamber is to the right tucked away in the corner. Achievement should pop once you finish this portal.