You Conduit!

To get this achivement, clear the trash in the corridor leading to Chief Corwright Kasreth in the Nexus Point Xenas dungeon. In this corridor there are 5 Corespark Conduits. Each party member needs to stand on one each (simultaneously) for a few seconds and then a Netherstorm Structural Cage will spawn near the middle of the corridor. All party members can then click this to unlock the pet Gortham and this Feat of Strength.

Edit: Requires level 90 to loot.

Edit 2: This FoS + Pet also seems to count toward the Mind-Seeker achievement unlock requirement of 17+ secrets, as it has its own trophy in the Seat of Knowledge as the "Record of Cuteness Overload".

Just confirmed with a guildmate that you can loot this pet and get achievement even if you were not in the original group to unlock it.

edit1: Yep, just helped 6 more get theirs

Can confirm , you cant do it with followers.
I tried standing on them to kill the conduits to see if it will work at the end when i was standing on the 5th conduit but it didnt worked.
Only works with a group of players