The once great builders of these temples are survived only by twisted versions of their creations.
The Temple of the Lost is an ancient laboratory created by an unknown civilization for the experimentation of biological organism. Unfortunately, it seems something happened either to the civilization itself or the experiments, because the lab is in ruins and infested with their aggressive creations. Fast, slow, lots of small damage or one large shot, these creatures are very diverse in their attacks and movements, so be prepared for a fight. On top of that, a mysterious green laser is shot every so often from strange machines, making the fight much more cramped at times.
The best gear for many shells are located here, but be aware- both Iratus and Thornmaster favor close quarters, and it's very easy to be swarmed in the compact rooms. It's advised to bring a large group of very skilled players, as one mistake can send anyone to their death.
The Temple of the Lost can be accessed by any one of its numerous doorways in Eschaton.
NSFW Meat-Sack of Doom
Thanks to: BagelWarrior
The midboss is rather easy to fight, as long as you do not get swarmed.
Appearance: A big eyeball surrounded with 5 or 6 (please identify) flesh(?).
Phase 1: Upon activating it, the midboss starts moving around, shooting yellow bullets that deal ~25 DMG, and spawning it's minions, which looks like live flesh. The minions can drop AMMO, HP and EC.
Phase 2: Once you dealt enough damage to a piece of flesh, more minions spawn, and the flesh disappears.
(Repeat Phase 1 and 2 until all flesh is gone)
Phase 3: Once all the flesh is gone, the eyeball starts to move medium-speed in a circle, shooting yellow bullets. Occasionally, it starts shaking, and resumes faster. Eventually, once you dealt the last hit, the screen starts shaking, and the midboss flies towards the door, breaking it and dropping a chest
Tips: Clear out the minions. If you don't, well, expect a huge swarm of them.
The secret tends to be found AFTER the midboss. The secret contains EC or stat boosts, along with one exotic item. In the elite variant, the exotic item will have one modifier. The secret tends to be hidden in the wall.
Another type of secret is the arcade. The arcade tends to be old-time flappy birds, shoot the enemy (or something along those lines), or other games (that I have not seen yet).
Like above, the shop tends to be found AFTER the midboss. It is found in an acid pit. However, in order to access it, you must find a switch (tends to be very close) and interact with it (will not apply to every acid pit in every Temple). Upon flicking the switch, the acid disappears and the entrance to the shop appears.