Subterranean Library by Than
The most Lost of all the Lost Chapters, this is Than's Knave-themed Quoth map, which even features a "Tome of Insanity," sort of like the titular Contract way when we were first introduced to the Library-world of Fodrian with Contract Revoked. The level is very large, and consists of a variety of rooms, halls and atriums in the Knave brick/bookshelf style, with interconnecting cavers featuring gaps into space and pools and rivers of blood. Because the whole complex is set inside caverns, it is actually a fairly unique take on the Knave theme, since the vast majority of Knave maps feature only manmade (or Elder-God-made, the point being no "natural" stuff like caverns) architecture. There are also some unique motifs that are repeated throughout the map, such as broken square towers, often hanging from the ceiling which looks cool, and other broken details. Overall, while I didn't think there were any stunning setpieces (the closest was the "find three buttons" area with staircases, jumping, and ruined towers), this is a consistently good looking map with excellent natural rockwork and a lot of detail put into the bricks/broken tiles/etc.
In terms of gameplay, the first thing to note is that secrets are definitely one of the highlights of this map. There are 20, and a lot of them are really cool. So exploration is definitely rewarded. Gameplay is fairly challenging, with many fights against droles and shamblers, and lots of ogres. However the balance of items is mostly good. I was close to out of ammo and health a few times, so you may want to play carefully. The one weakness of the map, I felt, was the layout. The layout was ridiculously intricate, you can see all kind of areas from other areas despite the fact that it is an indoor map, and you will always find yourself looping back to a familiar place from a new angle. However, due to the fact that there isn't a lot of variation in texturing or the style of the areas, and the map is quite long (getting both keys and getting runes, plenty of backtracking), it is fairly easy to get lost, or at least I got lost more than once. It could be just me, but I also remembering having difficulty navigating Plumbers Don't Wear Ties as well, and I think more signposting, messages, arrows, or even shortcut teleporters would help the player navigate these big but somewhat cramped indoor/underground maps. It might be just me, and this is the only weakness I thought the map had; otherwise it is an oldschool blast right out of the Lost Chapters, with plenty of secrets and some badass details like the floor giving way to pools of blood.