Scrying is the name given to using divination to discover hidden knowledge or future events, especially by means of using bones and stones.
To scry the person has to hold the stones and bones in their hand while they will their mind to quiet and empty, they will then feel a tug through their body that hauls them to whatever it is they wish to see.
When Feyre Archeron seeks the Suriel to ask him how she can find Hybern's army that the King of Hybern was hiding using the Cauldron. The Suriel tells her that Elain can find them, to which Feyre replies that she cannot see past his magic. The Suriel then tells her to use Nesta to track the Cauldron because like calls to like. Since the King of Hybern does not travel without the Cauldron, where it is, he and his army will be. Since Nesta is unskilled the Suriel suggests they scry using bones and stones.
When Nesta is scrying the Cauldron feels her spying on it and it captures Elain Archeron.
When the Inner Circle is in search for the Dread Trove, they think Elain could use her powers to try to See the Trove, but in the end, Feyre asks Nesta to scry again as Elain would need to dust off her powers which she hasn't used for a while. Nesta is reluctant to use her powers again since the last time she did it caused Elain to get captured, and her sister Feyre was at risk when she retrieved her from Hybern's camp. She reluctantly agrees to do it to spare them having to use Elain and risk her. Despite her agreeing, she stalls because she doesn't feel capable.
One time while Nesta was attempting to go down the stairs of the House of Wind, the House conjures two flat oval stones and three chunks of age-browned ovine bones, trying to encourage Nesta to scry. She says she can't but the House sends a breeze in reply as if to ask "Why?", to which Nesta replies that bad things happened last time she did, so the House vanishes the items.
The Inner Circle begins to worry because Nesta is not scrying so they think they might have to resort to other routes and give Nesta one more week. Nesta finally tries to scry for the first time, she sits in the House's private library with Cassian by her side and a map of Prythian before her. She asks the House for the stones and bones, and the House conjures a small earthenware bowl filled with the items. Nesta tries to scry but it's unsuccessful. That night she has a nightmare that makes her powers flare, and only Rhysand and Cassian are able to help her calm down.
The following day, despite what happened Nesta decides to try to scry one more time the next night. She tells Nesta he wants Rhys, Amren, and Az to be present. The following night they go to the River House and enter the study where they find Rhys, Feyre, Azriel, and Amren waiting before a giant map of the faerie realms, and a giant bowl of stones and bones beside it. This time she is successful despite wandering a bit far and almost getting lost while scrying, only Cassian, her mate, is able to bring her back.
- This practice also exists in the real world.