Legend of Grimrock

Excerpt from https://steamcommunity.com/sharedfiles/filedetails/?id=146481386 by MushaConvoy

Knight in a Shining Armor - Collect and wear full set of Valor armor (6 pieces).
You need to have all 6 pieces of Valor armour equipped at the same time. The Valor armour is the best Heavy armour in the game. If you have a party member that can equip heavy without penalty, this is the one to use. Pieces can be found:

Level 8 - Boots of Valor. In an alcove past a large number of poison switches accessed from a pit from Level 7.
Level 8 - Helmet of Valor. Found behind the Iron door.
Level 10 - Cuirass of Valor. Found in a secret room accessed from a pit from Level 9. The secret requires 3 torches and 2 rocks to complete.
Level 10 - Gauntlets of Valor. Found in an alcove in a south-west hallway.
Level 10 - Greaves of Valor. Found in an alcove in a south-east room.
Level 11 - Shield of Valor. Reward for completing the Fighter’s Challenge accessed from Level 6.

Excerpt from https://steamcommunity.com/sharedfiles/filedetails/?id=146481386 by MushaConvoy

Ninja Style - Collect and wear lurker’s wardrobe (4 pieces)
You need to have all 4 pieces of Lurker armour equipped at the same time. The Lurker armour is ideal for anyone wishing to evade attacks, I strongly recommend it for your front two rogues. There is unfortunately only one set. The pieces can be found:

Level 1 - Lurker Boots. Behind a secret in the room you start in.
Level 5 - Lurker Vest. Behind the Iron door.
Level 7 - Lurker Pants. Found in a secret room after falling through a pit in the Halls of Fire on Level 6.
Level 9 - Lurker Hood. Found behind a tapestry on the wall in a room with two Shrakk Torr (wasp-like enemies).

Excerpt from https://steamcommunity.com/sharedfiles/filedetails/?id=146481386 by MushaConvoy

• Find Zhandul’s Orb.
  Zhandul’s Orb is one of the better mage equipment, increases damage with fire-based spells. Requires 10 Spellcraft to equip. Zhandul’s Orb is located behind an Iron Door on Level 9. This door requires a Bone Amulet in order to open (there are two in the game, just grab one when you find one).

Here's a video

Excerpt from https://steamcommunity.com/sharedfiles/filedetails/?id=146481386 by MushaConvoy

Dismantler - Find Dismantler.
Dismantler is the best sword weapon in the game, randomly dealing additional shock damage, requiring 15 Sword skill. It is located in the Vault section of Level 8, accessible only from a secret staircase on Level 7. Dismantler is located in a secret area, required for that achievement.

Here is a video showing you how to get it: