Lukki Lair

The Lukki Lair is a biome found to the west of the Underground Jungle and The Vault. This area will always have the darkness biome modifier on. So, while you can see through the darkness without the All-Seeing Eye perk, areas you left will quickly get dark once again. It is extremely dangerous and unless the player has reliable means of taking down the Toothy Spiders, it should not be wandered into.

The Lukki Lair is a tight cave system composed of much more durable versions of materials seen in the Underground Jungle; mostly lush ground with chunks of flammable barren soil. In addition to that, there are many pools of ominous liquid of various sizes. In addition, fungus can be found in here, although in smaller quantities than in Fungal Caverns

The biome seem to have quite a few Extra Max Health pickups laying around, and the Wands are at least as powerful as the ones found in the Underground Jungle.

Survival Tips
To navigate this biome more safely, a good source of slicing damage is recommended. Chainsaw on a ranged Trigger is very helpful for two reasons: First, the huge Toothy Spiders are vulnerable to this damage type. Second, slicing damage increases blood output of slain enemies, such as the Headless spider. This creature bleeds Worm Blood for you to consume to greatly increase your view radius, and with some careful rationing with a spare Empty Potion, it should last for the entire visit. The spiders are also susceptible to ice damage from spells like Freezing Gaze, but this will prevent them from bleeding.

A handly source of large amounts of Water is also very helpful, as it's not easily found here and necessary to wash off any poison stains you might sustain from the Ominous Liquid. Water Trail is ideal, but simply overwriting the poison with another stain (such as Slime, either from the spiders or slime mist) will also work.

Finally, some means for effective digging should be considered. The purple variant of Lush Ground found here is very compact, and even rapid fire Luminous Drill will take some time to chew through it.

Points of Interest
At the top left of the biome is a small Wizards' Den area. At the very bottom is an Orb Room.

Enemies

 * Headless spider
 * Toothy spider
 * Shadow Bubble
 * Spider
 * Daddy Longlegs
 * Safety Drone
 * most Master Mages

... and more

Connected Areas
The biome connects the Underground Jungle with The Vault, and can be used to bypass the Holy Mountain in between.

If players can dig through Extremely Dense Rock, by mining down and slightly to the left from the Orb Room, they will find a room with a portal to the Tower. Reaching this area normally requires going through a significant portion of Temple of the Art.