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You must avoid triggering portals as you traverse the dungeon whenever possible. There are 34 portals throughout the entire dungeon, but they are broken up in the different parts of the dungeon.
A team with mics will succeed with this challenge as well as moving in a straight line and not spreading out. Have 1 person pull mobs to the group, don't have the group go to the mobs. There are a few portals you will have to engage to progress. Companions will not aggro or activate any portals.
Section 1: Blue Fire Pit Portals: As you travel through the first part of the dungeon you may see these on the ground along your path. Follow the path below as best you can; there are only 6 of these fire pits in this section.
At certain points, pull mobs to you in sections without portals around you; try not to engage enemies in spaces near portals! You will have to engage at least one portal in this section which is at the end, closest to the door. It is your choice if you want to go left or right, but you can't go down the middle otherwise you'll activate both!
Section 2: Stonehenge portals: These are easier to avoid in this section and there are 12 in total. Follow the path provided as best you can, and improvise if necessary! Before going down the bridge there are 2 portals relatively close together, you can't go between them, but you can go around the back left of them. If you activate one, you should be ok as this should be only your 2nd activation.
Section 3: Mushroom Portals: There are lots of these over the last 2 parts of the dungeon, so choose your path carefully; thankfully the aggro range is lower on these. There are 16 portals in total with a concentration of them near the end.
Shortly after the 2nd boss fight and the camp fire; there's a narrow hallway with a group of enemies and just behind them is a mushroom portal. So don't run in; pull the group of enemies out. You can hug the left wall to avoid the mushroom portal, if you activate it, you should be ok.
After that is the section with the Tomes and there are 5 more portals, you can pick up the Tomes without activating any portals. After the first Tome and you head down the ramp; there's a mushroom portal on the right, you can jump over the rocks on the left to avoid it! Once over the rocks, pull mobs to that spot, then have 1 person get the Tome up the hill, then double back. I marked one Portal Activation if you need room to maneuver to get around the remaining portals. After the bridge there is 1 portal followed by the cliff to the bottom floor. There will be 9 portals in the last section, but you can basically stay in the middle and not activate any.
If you choose the right path, everyone stays in a line and doesn't stray, you can get through this while activating no more than 2-3 portals. When I went through, we activated 4 portals in total, and one of those was on accident. However, some PUG is not going to pull this off, this would be near impossible with no communication. The achievement will pop after Nostura is defeated!