The entrance to this dungeon is hidden in the 2nd acid pit of the Nexus dungeon and requires you speak to Ned the Clever in Zaikhal first. You will not be able to reenter this dungeon after completing the quest (speaking to Ned after having handed in the resonator). After speaking to Ned in two weeks you can again enter (new resonator). The hollow minions hit very hard and the virindi will counter buff against vulns, they also drain health a lot.