Previously known as the Vellum Citadel, the archive and ancestral home of the Sages is now the site of a volcanic crater. Eruptions of lava began during the conquest of the Tiers, after Kyros' forces failed to claim the library in the Overlord's name. Kyros cast an Edict of Fire to break the siege and rid the world of the forbidden knowledge stored there. The Citadel has been a smoldering ruin ever since.
Welcome to the Library; hope you brought burn ointment. Find Foul Murmur torturing Folant to the northwest. Picking a fight with him means turning the whole camp hostile.
To the north of Foul Murmur and Folant is a plateau, which can be accessed from the upper ruins if you gave the Sages warning before casting the Edict of Fire during Conquest. Interact with the cross formations to gain the Sigil of Frostfire and +5 to Control Fire. A hidden container has the Emberglow Hood.
In the center is the Chorus camp around the entrance. The containers have minor loot, while the area near the entrance to the upper ruins has The Censor and Jelena (she only appears in the Disfavored path).
Welcome to the finest place of higher learning in the Tiers! Excuse the dust. Lantry will remark on the forcefields when you enter, indicating that you need a specific sequence to unlock them. Further along he will point to the lake of lava, noting that it was where the Sages made parchment, down to the vats of rendering fat.
Further along you'll find a Sage feigning death (sarcastically remarking that they're so obviously dead earns favor with Bleden Mark). Asking to bind his wounds earns the opposite. He will point you to the pass-phrase, or rather, the first part of it. Pick the incomplete passphrase from the shelves (42 Lore required).
Use the nearby pile of rubble to grab the ink-stirring pole. Return to the first barrier and dispel it (interact with it once it changes to the sigil symbol).
Fat Ulsten lurks around the corner. Further still is Gaptooth. To the northwest is an exit onto the plateau with the magic cross formations (only available if you warned the Sages in advance). The Emberglow Hood is there. By touching the magic cross formations, you can learn the Sigil of Fire.
You can enter the Scriptorium with 44 Athletics. The Sage here carried a potion recipe for research at the Library Spire.
Beyond Gaptooth's little abode is a rope and pulley that allows you to slide down to the lower levels.
Continue south-west. Mind the trap. Loot the Research: Magic Sigil book from the shelves. You can divert to the island with the Scourges by jumping the lava gap with Athletics 49 and get some scrolls for your trouble.
Over the small bridge of lava is another section of the Library. If you want to save the two Maric Oath Bound, spring to the south-west and attack the beastwoman, preferably taunting her and her support to divert their attention away from the scout.
Defeat the nearby Bane and pick up the third part of the passcode. Head up the collapsed floor to the upper ruins.
Climb over the rubble piles (42 Athletics) to reach a Sage and an Oath Bound. Oh and the final part of the passcode. Watch Lantry flip out over the prospect of seeing the Silent Archive, then take a swig of one of his inks.
Rescuing the Sage and Oath Bound will net you 500 rings ( 5 ).
Use the pulley to the northwest to descend to the entrance to the Silent Archive storage area.
Lower ruins revisited
You arrive near the ward protecting the entrance to the Silent Archive. Wipe out the Bane to the south-west. Head to the barrier and kill whichever gang boss you left alive. Activate the runes as per the completed passphrase: ↑ ↓ ← → (Sigils of Vigor, Fire, Force, Stone).
On non-Disfavored paths, you have the option of swapping an artifact for the Silent Archive, after reading the two sets of notes found around the Archive. Doing so ensures that the Library remains standing after the Edict of Fire ends. After the Edict ends, an area previously flooded with lava will now be available, but it's guarded by some Magebane.... and a Havoc.
On the Disfavored path, you'll not be able to save the Library. In fact, you can complete the destruction of knowledge by dropping the Silent Archive into lava.
Hammer of Sunder: Located in the SW corner of the Burning Library. Area only accessible after the Edict of Fire is broken and the lava recedes. Naturally, this requires you to not destroy the library; it is thus inaccessible in a Disfavored run.