Within the world of The Elder Scroll V: Skyrim there are also nine different masks that allow you to acquire new skills and upgrades. All masks are related to ancient priests who brought the object with them in the tomb, so when we reach the specified place we must reach the tomb of the priest, open it and beat the soul of the dead man to be able to collect the mask among its rubble. Below you can find useful details, places and videos that show you the positions of all the masks, including the ninth that will be obtained only after collecting the first eight.
Volsung Mask

Material: Corundum
Location: Volskygge (South of the Pinefrost Tower)
Typology: Light Armor
Armor: 23
Weight: 9
Value: 4611
Skills: Better prices, breath in water increased by 20%, weight carried increased by +20
Krosis Mask

Material: Iron
Location: Shearpoint (North of Fellglow Keep)
Typology: Light Armor
Armor: 21
Weight: 5
Value: 1615
Skill: 20% bonus for burglary, archery and alchemy skills
Vokun's mask

Material: Steel
Location: Ruins of the Great Gate (West of Solitude)
Typology: Heavy Armor
Armor: 23
Weight: 9
Value: 2182
Skills: Alteration, evocation and illusion spells increased by 20%.
Mask of Otar

Material: Malachite
Location: Ragnvald (Northwest the Markarth)
Activation: To unlock the tomb of Otar you must collect the two Torsten Skull's Key inside Ragnvald to be placed over the two slots next to the tomb.
Typology: Heavy Armor
Armor: 23
Weight: 9
Value: 1521
Skills: 30% bonus for resistance to fire, ice and energy spells
Hevnoraak's mask

Material: Iron
Location: Valthume (East of Gloomreach, south-west of Markarth)
Activation: After discussions with Valdar we activate the bowls and sit on the throne and wait for Hevnoraak's soul to awaken.
Typology: Heavy Armor
Armor: 23
Weight: 9
Value: 891
Skills: Immunity to poisons and diseases
Rahgot's mask

Material: Oricalco
Location: Forelhost (Southwest of Riften)
Activation: We open the door with the claw through the combination Wolf, Owl, Snake.
Typology: Heavy Armor
Armor: 23
Weight: 9
Value: 962
Skill: Resistance +70
Morokei Mask

Material: Moonstone
Location: Labrynthian (Southwest of Morthal) - Same place where the last quest of the Winterhold Academy takes place.
Typology: Light Armor
Armor: 5
Weight: 4
Value: 637
Skills: Magicka regenerates 100% faster
Nahkrlin mask

Material: Ebony
Location: Skuldafn (Beyond the portal of Alduin) - The place will be reached with the main mission "The Wold-Eater's Eyrie".
Typology: Heavy Armor
Armor: 23
Weight: 9
Value: 2173
Skills: Destruction and Regeneration spells require 20% less Magicka, bonus +50% Magicka
Below you can find a video where all eight places of the first eight masks are collected.
Collected the first eight masks you can unlock a ninth that will give us a unique ability, the Privilege of Konahrik, a special spell that can be activated when we have little health that will knock out the enemies and heal us and our allies.
Konahrk Mask

Material: Gold
Place: Labyrinthian (Southwest of Morthal)
Activation: We reach the altar and collect under it the wooden mask and the letter on the ground. After collecting the paper we put on the wooden mask to find ourselves in another time. Here we will be able to place the eight masks of the priests that will open a hidden compartment where the ninth mask is located.
Typology: Heavy Armor
Armor: 24
Weight: 7
Value: 3200
Skill: Unlock Konahrik's Privilege