Assassin's Creed Valhalla Opals can be found in the world or obtained by completing contracts.
As you explore England and beyond in Assassin's Creed Valhalla, you'll stumble upon all manner of loot, including Opals. These appear as bluish-white pulses when you trigger your Odin Sight, and are often collocated with a small cache of wealth (the little yellow dots that appear when you zoom in fully on the map, and don't count towards progress. area), or near an artifact (the white icons). Opals can also be found on their own in the world, and if you see a cave entrance in the wild, it's a good idea to lean your head inside.
However, the opals found this way don't match much. Every opal you find in the world is just that, opal. Most items in The Thousand Eyes stores can hold close to 120 Opals, so if you want to grab what you want on time (items are scheduled daily and weekly) you will need to take out contracts. Contracts are available from the various The Thousand Eye vendors scattered across England, which are indicated on the map by a Nordic node icon in Assassin's Creed Valhalla. They can be found in major villages and towns, and in your settlement.
Each supplier will have a selection of contracts, and these are all relatively straightforward deals. Most involve going to a place and then killing / finding someone. The Daily Contracts in Assassin's Creed Valhalla provide 5 Opals, while the Weekly Reward 20. To put it bluntly: you'll want to grind them daily to maximize your Opal Stores, then sit on them until something you get. absolutely dream appears in The Thousand Eye Shop. One final note: you will need to be connected to the internet not only to access The Thousand Eyes store in Assassin's Creed Valhalla, but also to contract Opals. Otherwise, you'll have to travel the world looking for those bluish pulses.
