Lost Artifacts and Web of Fate markers are two of Shadow of War's customary array of collectable items that are revealed on your map when you purify Haedir Towers.
Collecting a full set of each collectable within a region will earn you a Skill Point, and collecting all of each type in every region will earn you an additional bonus. A complete set of Lost Artifacts will earn you the Prospector skill upgrade, whilst Cluster of Spiders is the skill upgrade reward for finding all Webs of Fate.
For other collectibles in Shadow of War, meanwhile, be sure to chase down the Ithildin Door poem solutions and Shadows of the Past to get the Bright Lord Armour set, too.
Lost Artifacts locations and how to get the Prospector skill
These items provide a bit of additional lore, and are usually easy to spot - they're marked by a big glowing icon floating in the air. Collecting all of them unlocks the Prospector skill upgrade that increases the drop rate of higher-quality gems.
For the most part they're located in plain sight, so just mark them on your map, fast travel to the nearest convenient point, and then head to the marker. The only tricky one is this one located in Seregost which requires a Drake to access - summon one, mount it, and position yourself just above the cave entrance, then dismount and you should land on the ledge below - it may take a few tries to get it as you have no control of your descent after dismounting, but it's doable.
Need more help? Our Shadow of War guide and walkthrough gives you an overview of everything you need, but if you need something in particular, we have pages on Shadow of War Fortress Sieges, how to earn Mirian in Shadow of War, a guide for how to import your Nemesis and Follower to Shadow of War, collectibles guides like how to get all Shadow of War Legendary Armour and Weapons sets, a list of Lost Artifacts and Web of Fate locations, and Ithildin Door poem solutions and Shadows of the Past, along with how to grind XP in Shadow of War to power through the tricky Shadow Wars endgame and get the true ending. Finally, there's Shadow of War's army building explained and the best skills and how to earn Skill Points.
Web of Fate locations and how to get the Cluster of Spiders skill
There are three of these located in each region. Simply mark them on your map, fast travel to the nearest convenient location, and then head for the marker.
When you collect one you will be presented with a fragmented image that you need to reconstruct by rotating it; the controller will vibrate more vigorously the closer you are to solving it, so start by rotating horizontally until you get a rumble, then rotate vertically.
When you've collected all of them a final one will appear in Cirith Ungol. Collecting the final piece unlocks an additional cutscene giving you some insight into what makes Shelob tick, and also unlocks the Cluster of Spiders skill upgrade allowing you to summon a horde of spiders to poison your foes in battle.