Turn and Face the Strange - Toussaint (Blood and Wine)
Quest Giver: A boy will approach you and give you a letter after you complete Blood Run
Other Requirements: Blood and Wine DLC
This quest will begin while exploring the town of Beauclair after completing the Story Quest Blood Run. A little boy will approach you with a letter from either Yennefer or Triss (depending on who you romanced) which will begin this quest.
Head over to the cemetary next to the Lebioda's Gate Signpost (southern end of Beauclair). Here you'll find a grave stone, pictured below, that you must investigate. Once you've investigated the grave follow the foot prints to the nearby path where they end and open your inventory and look at the map that Yennefer/Triss gave to you.
After examining the map the quest will update and send you to an area in the water northeast of our current location. In the water you'll find some Elven Ruins and in those Elven Ruins will be a portal which will take you to the laboratory that we need to go to.
You'll encounter some spikes on the floor in the laboratory that you'll either have to jump over or wait until they go down and run across. At the end of the spike path before you go down the stairs make sure you go across the last optional area of spikes. It'll lead you to a treasure chest with a bunch of crafting goodies.
When you get far enough down you'll pass by two cat statues that will activate and attack Geralt; defeat them then continue further into the dungeon. There will be a hole you can drop down into that leads to a bunch of cramped tunnels, at the end of one of these tunnels is where you'll find Professor Moreau's Diary (pictured below).
Next to the diary climb onto the boulder and into the room with another Guardian statue. Defeat it then pass through the southern most doorway. In this next room you'll find a zip line that goes down to a lower platform (that you can't use) as well as four "blocks" on the walls that glow red when you use your Witcher Senses (pictured above).
What you'll have to do in here is use your Crossbow or Aard to hit all four of the blocks glowing red, this will open the door for you. The next room you come across will have many Gargoyle statues surrounding one larger human statue in the middle. Defeat the Gargoyle that attacks you and loot its hand. Place the hand on the pedastal right in front of the human statue to reveal the way forward.
Placing the Gargoyle Hand on the pedastal will cause portals all around the room to spawn. Look up at the large human statue in the center of the room and the direction she is facing. Always enter the portals she is facing to advance forward - any other portal will take you back down to ground level.
After going into the portal on the third level you'll finally stumble across the Laboratory that we've been searching for (pictured above). Inside of here you'll want to inspect the Megascope (near the stairs where I am standing in my picture) and retrieve the two Megascope Crystals that it is missing.
Technically you only have to watch entry #5 using the Megascope but you'll receive experience for watching all of the optional logs as well. Once you've watched #5 the quest will update and you'll have to go through a small tunnel in the back of one of the cells.
Megascope Crystal Locations: One on Table (by machines) and one on the bench (by prison cell)
Tip: Be sure to thoroughly search the laboratory. You'll find a few Greater Mutagens lying around
In the tunnels you'll have to battle centipedes (pictured above). Without the right strategy these are a real pain to deal with - you can only attack them from the front (they have armored backs) and they love to burrow around, not staying above ground for long. To easily defeat them use Yrden and force them to surface within your circle. This will paralyze them and leave them vulnerable to you.
You'll find the mutated centipede abdomen that you need at the southern most portion of the quest circle. Look for the eggs on the ground. Once you've acquired the centipede egg climb up the few ledges to reach a wall you can Aard through. This is a short cut back to the laboratory.
Back in the lab put the Centipede eggs into the back of the machine then strip down naked and jump into the machine, as shown below. Afterwards all you have left to do is leave the dungeon to complete the quest.