After a glorious battle against the Faceless (and a cowardly escape towards the Institute's elevator), I descended into the Deep Caverns and talked to Six. He explained what to do, where should I go, and also directed me towards a nearby cavern full of man-eating fungi: to search for something useful against Tchort's minions and his gate.
Now, I explored said cave, fought against the unfriendly fauna, and also probably destroyed the source of said monsters (something big and red called 'Pulsating Roots'), yet, I still have no clue about what I'm supposed to do now. I tried making my way down the tunnel towards Tchort, but his debuff and servants always make short work of my character.
Am I missing something?