Portal Stones are certain kinds of gateways to different locations and alternative realities within the Pattern. One Power is needed to activate them, with the same strength level as needed for Travel. Provided the user knows the meaning of its guiding symbolism, one stone can take the traveller to a stone of another location of the same world or to another stone in a different reality (e.g. to a parallel world of the universe of the Wheel of Time). When used for travelling in this world, the time dimension could be inconsistent.
Lanfear shares with Loial that "There are worlds where it is time rather than distance that changes. Spend a day in one of those, and you might come back to find a year has passed in the real world, or twenty. Or it could be the other way round. [...] This one seems pale to us because it is a weak reflection, a world that had little chance of ever being. Others are almost as likely ours. Those are solid as our world and have people. The same people. [...] You could go to one of them and meet yourself. The Pattern has infinite variation, she says, and every variation that can be, will be." 
They look like large, cylinder shaped, polished grey stones, about three spans high and a pace wide, covered with hundreds or thousands of archaic characters and symbols. The known ones described as standing in a hollow and having concentric steps around them coloured from blue to red, "one for each Ajah". When Rand touched one it felt curiously slick, like oiled metal, although it was dry.
They were created before the Age of Legends. Aes Sedai of AoL who could Travel, used them to journey the other worlds to study them. Studying of Portal Stones paved the way for the formation of the Ways; it is believed that perhaps the Ways are even in another, otherwise empty world, found by a Portal Stone. No one is sure; the information is long forgotten.
When Rand uses one with the help of Verin, she recites a quote:
"The Lines that join the Worlds That Might Be, laid by those who knew the Numbers of Chaos" which is a reference to a body knowledge which was required to build the Portal Stones and was passed from Age to Age. The book Mirrors of the Wheel is known to be written about the worlds and it is generally thought that no copy of it survived the Breaking whole.
Loial is also able to recall a memory of a piece of an old book, just a few pages he had seen where there was a drawing of a very similar stone with the following: "From Stone to Stone run the lines of "if", between the worlds that might be." The book also said that the Stones came from an older Age then AoL and even the Aes Sedai did not understand them, though they used them.
On the continent of Seanchan, Portal Stones were used to bring creatures such as grolm and raken from other worlds to aid in the fight against Shadowspawn  before the arrival of Luthair Paendrag Mondwin; these animals are now a regular part of the Seanchan army.
A Stone might not contain symbols to every existing World. It is also believed that there were Worlds without the possibility to visit through Portal Stones.
Not just the strength level counts, but the amount of Power used seems to be connected to the number of people moved through the gateway. When Rand takes the Aiel and all their belongings from Tear to Rhuidean he uses a small angreal with the look of a round bald man to have enough Power to take everybody with him. Although he manages, he almost burns himself out during the process.
Usage of a Portal Stone
Symbols on the bottom half symbolized other locations of the same world what is known as reality in the Wheel of Time universe. Symbols of the top half stood for other worlds or alternate realities, other dimensions.
Each symbol corresponds to another stone in the 'network.' By channeling into the appropriate symbol of the target world the Portal Stone activates.
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During the hunt of the Horn of Valere Rand, Loial and Hurin accidentally chose a half-buried Portal Stone to make camp and sleep there. Rand unintentionally channels during his falling asleep which activates the Portal Stone and they wake up in an alternate reality with their horses and belongings, but the Shiennarans were gone. Soon Lanfear appears, disguising herself as Selene. As this is a parallel dimension of their reality, Hurin is still able to follow the scent of the Trollocs. Later, with the help of Lanfear/Selene, Rand uses another Portal Stone in that alternate reality to take them back to their world.
"An exhausted sleep finally came, and with sleep, unbidden, the void surrounded him, flickering with an uneasy glow that disturbed his dreams." 
When Rand is trying to get to Falme, he uses a Portal Stone again, this time willingly, but unfortunately they are also moved forward about four months in time. It is not clear whether this was just the normal side effect of the use, as it is known that using the stones in reality the time dimension could be inconsistent , or Rand's channelling caused it.
In The Shadow Rising Rand uses a Portal Stone to transport himself and his party of Aiel from Tear to the Portal Stone near Rhuidean. This time he uses a small angreal with the look of a round bald man to have enough Power to take everybody with him. Although he manages, he almost kills himself or burns himself out during the process.
- Near Hardan
- Kinslayer's Dagger
- There is one near at Rhuidean on the slopes of Chaendaer and possibly at least one other in the Aiel Waste
- There is one near Stedding Tsofu
- There is one on Toman Head
- Four are located near Tear
- There is one along the Jehannah Road
- The Great Hunt, Chapter 16
- The Great Hunt, Chapter 37
- The Wheel of Time Companion, Seanchan.
- The Great Hunt, Chapter 13
- The Great Hunt, Chapter 11
- The Wheel of Time Companion, Portal Stones
- The Shadow Rising, Chapter 23
- Towers of Midnight, Chapter 41
- The Great Hunt, Chapter 17
- The Shadow Rising, Chapter 22
- The Great Hunt, Chapter 36
- The Dragon Reborn, Chapter 22