Follow the tunnel, watching your steps because there is a slope ahead that leads to some spikes and a lava pit. Slide down from the left hand side of the slope and jump on the platform. From there, jump over the lava pit to land on the safe ground. Alternatively, you can slide down the slope, but make sure you do it from the right hand side in order to avoid the first spike that comes from the left. Then jump before reaching the second spike, and depending on your angle, if you do not fall into the pit, you will land just at the edge of it on the other side. Then crawl beneath the spikes. Continue down to enter the lab.

Into Eckhard's lab - The third Periapt Shard is located in the toxic pool of the second room. So, in order to be able to access it, you need to do some things first. Go up the steps on the left hand side and get the Alchemical Phial #1 (Alchemically Purified Oxygen) from the small table on the right hand side. Crawl under the wooden platform on the left and get the Small Medipack.

Return back to the middle of the room and pull the lever close to the swinging cage to open a trapdoor beneath the cage and another trapdoor which will let you climb up the ladder on the right hand side. This also alerts two knights. Risking to be sounded boring, you can take them down, but why to bother with them, anyway? Also, avoid the water beneath the cage because it contains toxic water that can kill Lara.

Climb up the ladder to the top and dismount to the right. Follow the walkway and notice the Large Health Pack on the left wooden beam above. To get it, face the Health Pack, take some steps backwards from the railing and take a standing jump to grab the beam. Pull up, get the Health Pack and take a diagonal standing jump to the wooden walkway below. Continue to the walkway and place the Alchemical Phial #1 to the receptacle.

Return back to the ladder. Instead of going down, jump to the top of the cage. Walk to the middle right of it and a trapdoor will open. Drop into the cage, but before getting the Phial, you may want to save your game because after getting it the cage sinks into the water and you may die. Pick up the Alchemical Phial #2 (Alchemically Purified Hydrogen) facing the cage wall that is beneath the opening. Once you get it, press forward to reach the wall. Keep pressing forward and Lara will start climbing the wall. Press the up and right direction keys at the same time to climb diagonally to the top, where the trapdoor is. Traverse to the left and pull up.

Stay at the top of the cage where you are safe and avoid the trapdoor which can drop you into the toxic water. When the cage sinks to the lowest point, climb in the alcove in the wall and crawl to get the Alchemical Phial #3 (Alchemically Purified Salt). Turn around, somersault to return back out to the cage and climb any of the other three walls. You cannot pull up, so press the Jump button to back-flip and land outside the pit. Place the Alchemical Phial #2 to the receptacle at the top of the steps (to the left of the entrance) and the Alchemical Phial #3 to the receptacle in the room with the toxic pool to the right hand side of the entrance, as you enter the lab.

After using the three Phials, a cut scene shows a glowing chemic shedding in the pool.

Jump in the pool and get the Periapt Shard. This opens a gate in the main room of the lab. Climb out of the water and go through the gate. Slide down the slope and open the door.

Fighting Eckhardt - There is nothing to pick up around the room, so approach the middle of it to trigger a cut scene.

The cut scene shows Eckhardt in progress to revive The Sleeper, but he realizes Lara and seems surprised that she is still alive. Lara says she is the only one who can stop him, but Eckhardt tells her that he is now immortal, as he has hunted down and killed the last of the Lux Veritatis. Lara shows him the three Periapt Shards but he does not seem to be afraid. Lara's last comments "D'you know it's going to be a real pleasure to shut you up".

Pleasure and easy as you cannot imagine. The first thing you have to know is that you cannot kill Eckhardt with your guns. As Kurtis told you, Eckhardt needs to be stabbed with three Periapt Shards. As soon as the cut scene ends, commando crawl (Duck+Stealth). There is no need to move around, just stay in that position. He will start shooting either blue energy or flaming bolts at you. As long as you stay down, you will not get damaged at all. After some bolts, Eckhardt will begin to create clones of him. Now you can stand.

There is a grated part on the floor, close to the energy shield. Stand outside of it (as shown in this screenshot) but do not back up a lot, because the energy shield will throw you back and cause you damage. After Eckhardt has created three clones, they will run to the small circle and fuse together (make sure you do not stand on their path). Now you have the real Eckhardt in front of you. Wait until he throws another bolt. If you stand on the grated floor, the bolt will kick you back. It is not a big deal, but it will take some time until Lara stands up again, which means that you will lose time and have to get through the same procedure again. Once he throws the bolt, approach him in the circle. Press Action to use one of the Shards. The hand-to-hand combat is activated when you press Action in front of an enemy and that's why you will see Lara kicking Eckhardt before the cut scene runs. If you do not make it on time, you will have to get through the same all over again.

(Bug note - In the PC version at least, do not save whilst Eckhardt is creating his clones. If you load this saved game, Eckhardt will start creating the clones from the beginning.)

The cut scene shows Lara stabbing Eckhardt with one of the Periapt Shards.

You now have two Periapt Shards. This means that you have to do the same thing two more times in order to beat him.

After kicking Eckhardt for the third time, the cut scene shows Lara running to stab him for the third time. Karel appears and stops her. Lara is surprised seeing him and Eckhardt asks Karel to kill her, but Karel finally kills Eckhardt. Lara is surprised, telling him that he worked for Eckhardt, but Karel says that Eckhardt worked for him instead, and that he (Karel) was helping her all along. To prove this to her, he starts getting the faces that Lara had met: Bouchard, Luddick, even Kurtis. Lara cannot believe in her eyes. He says that he is a Nephilim and asks Lara to join him and built the new order. At this point, Lara sees a symbol in his palm and flashes back to Werner's murder.

In this FMV Lara remembers more. Eckhardt seems to ask Werner why he did not bring him the last Obscura Painting but Werner tells him that going after it would be too dangerous and Lara could do it. He then kills Werner and transforms into Karel whilst crushing Werner's glasses. She then sees the symbol in his palm.

In the cut scene back to the present, Lara tells Karel that he was the one who killed Werner. "Too many people have died for me to trust you". Karel says "Stupid mortal. So be it".

Fighting Karel - Now you have to destroy Karel. You cannot kill him with your guns, so for now avoid his green bolts by commando crawling (or simply run). Go to Eckhardt's body and get the Eckhardt's Glove. Use the Glove to the receptacle behind the column on the left of Eckhardt. When you use the Glove, two ladders will lower. Since the one behind to the left is closest, climb up it.

Follow the walkway to the left to find another ladder to climb. Climb it to the top and follow the walkway around to find another ladder. At the top, follow the walkway to reach a part where there are no railings. Step on the metal ledge and jump towards The Sleeper.

The FMV shows Lara grabbing the leg of The Sleeper. She uses Kurtis' shuriken and places it towards The Sleeper's leg. She then back flips and The Sleeper is getting destroyed by a strong blue light. Along with The Sleeper, Karel dies too. Lara then approaches the middle of the room collecting Kurtis' shuriken. It then shakes popping out blades (something that only Kurtis could do whilst calling it). It makes Lara turn towards a dark tunnel. She holds it, smiles mischievously (like she knew what just happened) and then disappears into the dark tunnel (probably where the shuriken showed her) to find... who??