With over 270 total quests available in Skyrim, there is a good chance that most players haven't seen every side quest on offer. Between the multiple guilds that can be joined, Hold quests to become Thane, and new quests introduced in the Dawnguard and Dragonborn DLC, many great quests can fly under the radar if you aren't actively looking for them.
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Some of these quests are simply fetch quests or require a bandit camp to be cleared out, while others give a rich backstory on certain events or characters in the game and are well worth completing for this along. Many of these side quests also grant unique rewards that make the quest worth tracking down and completing as well, some of which are particularly powerful items.
10 The Pale Lady
When walking past Frostmyre Crypt for the first time, you may end up in the middle of a battle between Elsa Blackthorn and a group of bandits who have turned against her. After learning that her leader stole a sword from the crypt you can begin the quest to investigate the massacre within. After reaching Frostmyre Depths, you will find a room with an altar and a Wisp Mother called The Pale Lady, who will attack you until you either kill her or place the Pale Blade back on the pedestal. The blade itself can be taken as a quest reward and is unique for having both an Ice and Fear enchantment on it.
9 The Man Who Cried Wolf & The Wolf Queen Awakened
To begin this quest, simply talk to Falk Firebeard, the Jarl's steward in Solitude, where he will give the Last Dragonborn the task of investigating a series of disappearances around Wolfskull Cave. Upon clearing the dungeon of its necromancer inhabitants and preventing their ritual from being completed, you can return to Falk for your reward as well as the second part of this questline, The Wolf Queen Awakened. This is a much longer quest that sends you to multiple locations, culminating in a confrontation against Potema, the titular Wolf Queen. After completing the quest, you will be rewarded with the Shield of Solitude, a unique leveled shield that blocks additional damage as well as granting magic resistance, with the most powerful version obtained after level 40.
8 Totems of Hircine
Before the Dawnguard DLC introduced the werewolf skill tree and the Dragonborn DLC brought several rings that improve their combat capabilities, the werewolf form was fairly underwhelming. However, you can also do a side quest for Aela, either after marrying her or by completing the Companions questline, called Totems of Hircine that further improve the werewolf from.
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Each totem grants a blessing to the werewolf form that gives it different abilities, such as Detect Life, summoning Wolf Spirits, or a Fear effect, all of which can be further improved through the werewolf skill tree. The location of each totem is radiant, however, and may cause the player to be sent to many different dungeons.
7 Kyne's Sacred Trials
After talking with Froki in his shack, southwest of Riften, he will task you with hunting down several spectral animals, including a giant Mudcrab and a spectral Mammoth, in order to prove that the player is a great hunter. After completing each hunting trial, the player is rewarded with Kyne's Token, a unique necklace with the same design as the Gauldur Amulet and increases Bow damage by 5% while decreasing damage taken from animals by 10%. The enchantment may not be all that powerful, but it is a neat combination of enchantments that isn't seen on many items in Skryim.
6 Salt For Arcadia
Although this quest in Whiterun is incredibly short, as the player is only tasked with taking delivering Arcadia a pile of Frost Salts from Farengar, you do get some neat potions for the deal. After asking Farengar if there are any other magic practitioners in Whiterun, he will give you the salts to deliver to Arcadia, who claims that she needs them to make a love potion. In thanks for the player's hard work, they will be given a Potion of Brief Invisibility, Potion of Enhanced Stamina, and Potion of Illusion.
5 The Ghost of Old Hroldan
At the Old Hroldan Inn, on the road between Markarth and Rorikstead, the player can encounter the ghost of Old Hroldan by spending the night at the inn. When confronted, the ghost asks them to find Hjalti's Sword and bring it back to them, with the sword itself being found in one of a few radiant locations that are usually full of Forsworn and Hagravens. When the sword is retrieved and returned to Old Hroldan, the player is granted a level in both Block and One-Handed, making it a quest worth completing for any warrior build.
4 The Raid & Supply and Demand
This questline can be started by talking to Wujeeta in Riften, who is struggling with a Skooma addiction and needs the player's help to kick the habit. After bringing information on Skooma smuggling to the Jarl's attention, they will send the player to eliminate those responsible, which will then trigger the second quest after defeating the leader of the organization.
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After finding a note on Sarthis' body and returning it to the Jarl, the player is then sent to the primary production facility of the Skooma smuggling business and tasked with eliminating everyone inside. After completing this quest, the player is given a random enchanted weapon, making it a good way to reset for a particular enchantment such as Absorb Health.
3 Unfathomable Depths
Also beginning in Riften, the player can receive a quest once they have reached level 14 or higher from a quirky Argonian called From-Deepest-Fathoms, who tasks the player with returning the Lexicon to a nearby Dwemer ruin. The dungeon is fairly standard among other Dwemer ruins, though the player is also given some back story on the last expedition to Avanchnzel that resulted in From-Deepest-Fathoms going mad. After returning the Lexicon to its pedestal, the player obtains the Ancient Knowledge power, which increases their armor rating when wearing full Dwarven Armor, though also has the tendency to glitch and increase the armor rating of all armor except Dwarven.
2 The Book Of Love
The side quest can be started in Riften, though the quest itself will take the player around most of Skyrim in the process of completing it. After talking to one of the Priestesses of Mara, the guest sends the player around the world to solve various problems of the heart, usually involving some kind of open gesture by one of the parties. After finishing the quest, players are rewarded with an Amulet of Mara and the Agent of Mara power, which permanently increases magic resistance by 15% and is one that no build can do without.
1 Lost Relic
Taking place during the Dawnguard questline, Lost Relic is a repeatable quest that tasks the player with exploring Skyrim to find various relics from the Dawnguard's past for Florentius Baenius. The quest itself is given three times at random and may require the player to complete other radiant quests between each outing, but completing each quest will reward the player with the Dawnguard Rune Shield, Dawnguard Rune Hammer, and Dawnguard Rune Axe. Each of these items is particularly devastating against undead enemies and is very useful in the Dawnguard storyline.