The three rings are a ter'angreal found in Rhuidean.
Appearance[]
The ter'angreal is made up of three gray, metal rings that stand vertically in a circle and are joined at the middle.
Use[]
The rings are used as a rite of passage for a woman becoming a Wise One apprentice. When one enters any of the rings, she experiences countless possibilities of her future based on every decision she might make. Most women cannot remember the majority of these experiences, although they remember the most important ones when they need it.[1]
Some women do not emerge from the rings, likely from not being able to handle what they see.
There are some similarities with the silver arches ter'angreal used by Aes Sedai in the White Tower to test a novice to raise to an Accepted.