- "And here in Rivendell there live still some of his chief foes: the Elven-wise, lords of the Eldar from beyond the furthest seas. They do not fear the Ringwraiths, for those who have dwelt in the Blessed Realm live at once in both worlds, and against both the Seen and the Unseen they have great power."
- ― The Fellowship of the Ring, Many Meetings
The Unseen are objects and creatures of the spirit world that belong to 'magic'. Some of the most obvious examples of Unseen creatures are the Ringwraiths, which were invisible and formless without disguises provided by Sauron.
Those who wore the One Ring went to the Unseen realms and could see the forms of other persons there.