The Bastion Stair (public) dungeon is one of the high level dungeons, you'll probably spend some time in. The Bloodlord set, which can be obtained from the bosses, has (like the Annihilator set) lesser wards, that will help inside the city dungeons and in Fortress fights. You best reach the dungeon through
the very NE corner in Praag, there is a portal which will take you towards Bastion Stair. The structure is actually located in the Chaos Wastes (far SE corner) where there is a portal as well, but access through Praag is faster from flight point.

The Bastion Stair has an entrace hall where you'll find a bunch of quest givers, a healer and the rally master that will grant rewards from Bastion Stair influence (you gain from doing PQs inside the dungeon). Like in Mount Gunbad you'll need enough influence to enter the private boss instances at the end of each wing - first inf bar for first boss, etc. The lockout (after you kill one of the final wing bosses) for Bastion is 1440 minutes. You can use /lockout to check how much time is left on the instances you got an active lockout. The whole dungeon got a Khorne/Beast/Demon theme.
The Bastion Stair consists of three wings:
# Trail of Carnage(left portal - mobs 33+)
There are three Public Quests in this wing:
1.
Rise of Carnage2.
Bloodherd Labryinth (nice typo Mythic)
3.
Trail of Carnage (Arena Challenges)
The final boss in wing 1 is
Thar'lgnan (drops Bloodlord boots).
Trail of Carnage MAP v1.0
(with connections and boss spawns)
# Path of Fury(right portal - mobs 35+)
There are three Public Quests in this wing:
1.
Fury's Ascent2.
Halls of Rage3.
Path of FuryThe final boss in wing 2 is
Lord Slaurith (drops Bloodlord shoulders).
Path of Fury MAP v1.1
(with connections and boss spawns)
# Steps of Ruin(stairs straight ahead up - mobs 37+)
There are three Public Quests in this wing:
1.
Step of Anger2.
Step of Hatred3.
The Brass LegionThe final boss in wing 3 is
Kaarn the Vanquisher (drops Bloodlord helmet).
Steps of Ruin MAP coming soon.As of patch 1.1a the Bloodlord gloves drop from golden PQ bags inside the dungeon.
There is also a fourth area, called the
Rift of Rage, located at the end of the third wing, where the last and fourth boss,
Skull Lord Var'Ithrok (drops chest & gloves), can be found. To gain access to the portal to enter the last private instance, you'll need to finish a few quests inside Bastion. The ones you need to finish for
attunement are
wing 1: Blood on the Steps (3 part quest), leads to
Leashing the Bull (kill wing 1 boss).
wing 3: Infinite Patience (4 part quest), leads to
Vanquishing the Skull Lord.

In each wing you can find skulls laying around on the floor, they are named after the wing you picked them up (
Skull of Carnage,
Skull of Fury and
Skull of Ruin). Those skulls can either be placed on pikes found throughout the dungeon - then they might yield a short buff or a curse - or can be placed at the respective skull piles near the entrance hall to spawn another boss called
The Collector. Apparently you need around 100 skulls from each wing or something along those lines to spawn him.
NOTE: This post is work in progress and will be completed/updated with maps of the other wings as well as more info. You won't find any spoilers how to kill bosses here tho. It's just to provide some orientation inside the dungeon. If you find any errors (some things i just wrote from memory) please let me know. If you can remember the exact names from the non PQ related boss spawns, leave a note as well.Update 24/11: Added the rest of the PQs and the map for wing 2.
Update 29/11: Updated the non PQ hero name for wing 2.
Update 13/12: Updated the patch 1.1a info about gloves.