This page contains the walkthrough for Scavenger Hunt: Grandmaster Manticore Gear, a side quest in The Witcher 3: Blood and Wine.

Walkthrough

You can pick up this side quest from the grandmaster smith Lafargue, whom you will meet at the start of the side quest Master Master Master Master!.

Once you have the quest, head to the first location which is the Bastoy Prison ruins, south of the Fort Astre Ruins signpost and southwest of the Chucote Cave signpost.

This location is shared with the quest Treasure Hunt: The Toussaint Prison Experiment.

Southeast of the ruins is a campsite (character marker).  There is no map marker but you can find a few lootable containers there.
While exploring the grounds you encounter a Hooded Woman who transforms into a level 42 Alp.  If you haven't met one before, it is a type of vampire similar to a Bruxa.  It is vulnerable to Moon Dust bombs, Vampire oil, Black Blood potion and Yrden.

Go toward the large building at the northeast of the ruins.  Looking up, you can see a catwalk around the tower.  The ideal approach is to start at the beginning of the catwalk on the northwest side of the tower.
Inside the tower there is a lootable skeleton.  Turn back toward the entrance and, to your right, there is a compartment holding the Manticore Steel Sword diagram and a Prisoner's Journal.  Read the journal to find the next location you need to visit.

Lebioda's Cave

Lebioda's cave is southeast of the Gelenser Farm and southwest of the Termes Palace Ruins travel markers.  On entering the cave you find a large room.  Go to the far end and activate Witcher senses to find Merten's Prayer posted on the wall.  Read it and you find that the prayer is written on the back of the Manticore Armor diagram.  You also discover the next stop for the quest.

Lebioda's Temple

If you have it, the Prophet Lebioda Statue travel marker is the best place to start.  Otherwise, Lebioda's Temple is northwest of the Plegmunds Bridge and north of the Castel Ravello Vineyard travel markers.
Enter the abandoned temple and, at the far end of the room, knock down the wall using Aard.  On the other side is the level 40 Great Beggar's Ghost (specter) that you can take out with Spectre oil and Yrden.  On looting the corpse you receive Bones of the Great Beggar.
This triggers the level 40 secondary quest The Words of the Prophets Are Written on Sarcophagi.  Since you are already in the middle of it, it's best to complete it now.
Continue to the far end of the area with Witcher senses active to find a small box glowing red.  Inside are the diagrams for Manticore trousers and boots, plus The Great Beggar's Journal.  Read the journal to discover the next waypoint for the quest.

Hidden Chapel

The cave with the hidden chapel is south-southwest of the Palace Gardens travel marker.  Wade/swim through the water and soon you encounter a violet haze that causes you to choke.  Keep going, it's not harmful.
But it DOES cause hallucinations.  As you move on, you encounter a (nude) "young woman".  As you get close to her you find out she is a level 40 Bruxa (vampire) and a second one quickly appears.  Or, bypass her to the left to avoid the fight.
Further in you need to jump up a couple of platforms, then see a group of beggars highlighted in violet.  Drop into the area to find a stash of 68 crowns.  Give each of the five beggars alms (10 crowns) and each disappears in a flash of light.  If you don't then an Archespore will appear and the beggars will vanish.
Continue into the cave and you encounter a ledge.  Witcher senses uncover a patch of red that seem to indicate treasure.  You also detect Kikimores so apply Insectoid oil to your silver sword and set up Igni.
Drop down and go right to find three level 40 Kikimore workers threatening a Townsman outlined in violet.  You can attack them while they are concentrating on the Townsman.  If you go for the "treasure" instead, you receive nothing and will be attacked by four workers.  Either way, the Townsman disappears after you slay the foes.
Move on to the next area where there are two platforms to jump and a wall to break down with Aard.  Past that, you find a Mystery Man, also outlined in violet.  As you approach he disappears but there is loot to check out.
The small box contains Merten's Notes and the Manticore Silver Sword diagram.  There is a small pile of (worthless) bones to examine on the stone altar.  Read the Notes to discover the final stop for the Manticore diagrams.

The Lake of Cleansing

The lake is east of the Dun Tynne Crossroads travel marker.  If you arrive at the small pier at the southwest end, you encounter three bandits who turn hostile when you approach.  After dispatching them, head to the end of the pier.  You can spot some loot nearby at the bottom of the lake using Witcher senses.

You might want to use a Killer Whale potion before diving because there are quite a few small lootable items near the large items.  Your target is a bag that glows red (Witcher senses) and contains Merten's Last Letter and Diagram: Manticore gauntlets.  Read the letter to end the quest.