The Drochaids are a network of portal locations sitting at wells of magical energy, where ley lines converge. Most cities are thus constructed somewhere near such a place. These wells serve to power the complex magic patterned by the symbol, the symbol is filled with pure silver laid into deeply carved fissures inside large flat stones. These stones are made of a solid and very dense volcanic rock which shines sparkling blue in direct sunlight, and a deep blue-grey in diffuse light.
No one is entirely certain who originally created the stones, but the knowledge has been passed down. Very few sites with the mystical blue stones exist at the current time, and none have enough to form even a single new Drochaid location. The most common idea on the theory of who created the Drochaid is that the Gods brought them down from heaven, and taught elves how to make them, who then taught man before the wars and the Peace of Ages.
The symbol engraved into the stone just called a Drochaid in silver pulls in magical energy and stores it in the the pattern for a portal to form, missing the final flows to form a portal from one stone to another. These can be used by anyone who has a Focusing Stone, which are relatively easy to fashion by a qualified mage which allows a persons thoughts to complete the magical pattern of the Drochaid and open a portal from one place to another.
Once activated, the magical energy swirls up and creates a vortex of silver-blue energy at both the origin and destination. If one is inside the vortex when it forms the vortex is short-lived and closes right after, leaving the person at their destination instantly. If no one is standing in the vortex as it forms, it will stay open until the focus is released. Since a Drochaid can only be used to go from one place to another at a time, it is actually against the law in most places to hold a portal open for long periods of time without a serious need to.
A focusing stone can be specific, opening a portal from one Drochaid to another specific Drochaid or they can be more general, allowing the owner to pattern the magical forces to a location of their choosing. It is most common that the owner of a Focusing Stone has to have been to a location before, to use a general stone to go there. This is not the case for a specific focusing stone.
The Airgid Drochaid's are extremely difficult to create, and only a mage of the highest order can even attempt it. It takes months to prepare the silver, and the stone carving must be done by hand without the use of magic. Once the stone is prepared and the silver is ready, the ritual to open the stone and silver to be joined takes 2 days to complete prior to being able to pour the silver into the stone. Once poured a second ritual is required to bind the silver and stone together and establish the final patterns of magic takes a solid week of continuous magical work to complete, taking no less than 14 mages joined in a circle to fuse the stone and silver together in such a way to complete the process.
All of this must be done on-site, at the location of a well that doesn't already have a stone in place.
Some locations are only known to exist because of the focusing stones to get there, rare artifacts which provide the only transport to these mythical locations. Often times these are forgotten places of old cities or fortresses. Many times legends are told in reference to some unknown site of a portal, leading to vast riches or vaults of magical power.