Hub 4: Forsaken Outpost

The Forsaken Outpost is one of the hub maps of Hub 4: Castle of Grief. There are two items on this map that you'll need to advance in Hub 4: Gibbet: the Liber Oscura and the Daemon Codex. You will also find access to the secret area Hub 4: Desolate Garden, if you crossed the trigger line on Hub 1: Bright Crucible and pulled the switch in the secret area of Hub 2: Shadow Wood, Hub 2: Sacred Grove. Otherwise the portal will be blocked.

You will find two items on this map that you'll need in Hub 4: Gibbet; the Liber Oscura and the Daemon Codex.

Two tomes of obscure and ancient knowledge lie forgotten within this base abandoned in despair that will help you in your quest.

First visit
You start off in a cramped cave with several enemies which depend on your character class. The Fighter will face Ettins, the Cleric will fight a mix of Ettins and Afrits, and the Mage will fight Afrits. The eastern passage contains some Mana. The cave opens up to precipice area, where there are Green Chaos Serpents and a building at the far end. You can jump across the platform, but it is safest to walk along the eastern wall. There is another platform with Discs of Repulsion, but it requires a dangerous leap - the Fighter and Cleric can make it, but not the Mage. It will become safer later. In front of you are a pair of doors - they open simultaneously to a courtyard full of Centaurs and Slaughtaurs. Be sure that they don't sneak up on you from one doorway while you're fighting in the other.

Once inside, there are two Green Chaos Serpents on ledges at the far/northern corners. Past the pillars in the north is a large door that requires the Rusted Key to open. A couple more centaurs may attack you here. To either side of the door, there are ascending staircases that lead up to the corner ledges. The northeast ledge has a Platinum Helm, while the northwest ledge has a Quartz Flask. To proceed, take the descending stairs to the left of the locked door. This takes you to a small room with a bullhead switch - pull it, and a new passage will open directly to the south. After fighting through the Ettins, you will come to the Liber Oscura on a pedestal. Once you take it, the walls will open on the sides to unleash many Dark Bishops. Be careful not to get surrounded - it is safest to run back out of the room, although you can also fight from a corner. Once they're defeated, you can pick up mana from the side compartments.

Moving on, you will return to the courtyard where new areas have opened up. Two Green Chaos Serpents will be there to greet you. The southeast corner now offers you the rusted key, which will allow you to enter the main door. There are also two optional areas, which are covered in the next paragraph.

The eastern wall of the courtyard has opened to reveal Crystal Vials, a bullhead switch and two elevators. Pulling the switch will activate the elevators, which release two Ettins. You can ride the elevators to get Discs of Repulsion in the southern room and Fléchettes in the northern room. The second area is a cavern which you can now enter from the southeast corner. It contains some Dark Bishops, and curiously an Afrit that is inactive in its invulnerable ball form. There are high and low areas here, but no deadly drops. If you fall, you can pick up Crystal Vials and get back up via the steps at the northern end. There are two platforms you can hop across to get between the western ledge and eastern ledge. The eastern ledge has a Porkelator artifact and a bullhead switch. Pulling the switch opens a passage at the far northern end of the western ledge. This leads to a small area with mana and your second weapon. To the left is a window looking into the area behind the main door - you can shoot through at monsters that are in range. Strangely, the window can't be seen on the other side. To the right is a metal barrier - it blocks an area that you won't be able to access until your second visit. For now, make your way back to the courtyard.

With the rusted key, you can open the rusted key door. Behind it, there is a large corridor with a small group of Ettins and Centaurs/Slaughtaurs. Be careful - after about 17 seconds, a large wave of Centaurs and Slaughtaurs will teleport in, and Ettins will be released from the northeast/northwest corners, so be careful not to get surrounded. You may find your ultimate weapon useful for clearing out the crowd. There are four wall segments at the sides with plenty of Quartz Flasks and Crystal Vials. Behind the segments, there are narrow corridors with more enemies. The northeast and northwest corners will have Fléchettes and mana. At the northern end is a podium with a metal barrier in place. To open it, you'll need to go into the four side chambers, accessible from the narrow corridors. After defeating the Ettins in each one, you can pick up the Discs of Repulsion and pull the bullhead switch. After all four are activated, another wave of Centaurs and Slaughtaurs will teleport in, and the metal barrier at the northern podium will open. Behind it is the Daemon Codex. If you fulfilled the prerequisites, instead of an Icon of Korax behind the book there will be a portal to the secret level Desolate Garden.

Now that you have the two books, you can make your way back. As you leave the courtyard and re-enter the precipice, you will find that the western platform is now easily accessible via a magic step. Be careful - you cannot run across, you must jump. You'll be able to pick up several Discs of Repulsion if you need them. The portal back to Castle of Grief is in the southern cave where you started.

Interestingly, there are Dark Bishops waiting low in the precipice, although they usually won't notice you. The inactive Afrit in the eastern cavern is activated when you've completed the visit.

Second and final visit
You will enter a small, chapel-like room. Surrounding you will be 6 stained glass windows, with a Dark Bishop behind each. There are Boots of Speed behind the center window on the left (south). The others have Mana containers.

Walk down the middle of the room to trigger a linedef. The torches light, and a message appears: “A door opened in the Gibbet”, meaning that the Axe Key is now available. Ahead, you’ll be able to move aside the iron barrier to access the rest of the level. From here, the most convenient path back to Gibbet is by returning to Effluvium.

Trivia

 * Liber Oscura can be translated as "dark book", "dark encyclopedia", or "book of darkness". Liber is latin for book, while Oscura is italian/spanish for dark/darkness (italian: third person singular present tense, spanish: feminine, latin root: obscurus).
 * Daemon Codex is latin for "demon book" or "book of demons".
 * There are many usages of Latin and archaic English in Hexen, which fits with the overall theme.