"Ah, yes, spellspun gates. Portals, some call them. "Death-doors" is the term I prefer. The reason? Well, each step through one is a step closer to the time when your death is standing waiting for you on the other side—with a big cold grin on its face and a sword in its hand you'll have no time nor chance to avoid."
— Bharajak Steelshar
A portal was a two-dimensional, often up to 15 feet (4.6 meters) circle, but not limited to it both in size and shape, area that was both intangible and invisible. Due to this, a freestanding archway of some kind usually was built to identify the location of a portal, so those who could not detect magical auras did not stumble into them accidentally. It was impossible to visually find out a portal's destination. For example, sticking one's head into that field to find out the destination was impossible, for touching a portal activated it.
One way to find out the location of a portal was to cast detect magic. The magical aura of a functional portal was much stronger than that whose uses were completely exhausted.
Passing through a portal was described as an unsettling experience: space between the "fabric of the planes" was entirely dark, devoid of air and offering no sensation of temperature. Oddly enough, it seemed to elicit phantom scents, like the smell of wintergreen or stale wine.
Portals were magical transportation devices. When somebody touched the two-dimensional field, that person was affected by a greater teleport effect towards a pre-set destination. This was the reason why the "sticking the head through"-method to find out the destination failed. Creatures could enter and be transported by a portal, as long as they could pass through them, and objects could not.
For example, one could not shoot arrows through a portal, they would not just not pass through, but bounce off.
An exception to this no-object-rule were those objects carried by creatures passing through a portal. However, even this had a limit of 850 pounds (386 kilograms) and the definition of "carried" was anything touched. This weight limit had the peculiarity that an object that was touched by several creatures dropped the amount of objects the creatures could carry by its weight for all and not just for one.
The limit on how many creatures could pass through a portal was the one that the builder set and the usual limit was as many creatures as wanted to pass through.
A portal could only send a person to its destination, but not back. Quite often, people built directly at the destination a second portal to effectively create a two-way-portal.
Destroying a portal was very difficult. Disintegrate or other physical means were not means by which a portal could be destroyed. Successfully using dispel magic could stop the working of a portal for up to twenty four seconds.
A portal's magic was very durable, but it was subject to wear. Portals could also be influenced by global magical catastrophes. Such portals started to malfunction. Malfunctioning portals were generally a century or older. When such a malfunctioning continuous portal was activated, the portal could start to show its malfunctions and applied such effects for up to a minute. Possible malfunctions were that the portal did not apply a greater teleport but a greater dispel magic effect to either the user or the user's magic items.
When the former happened, the target was the user and could lose magical effects he or she was benefiting from.
When the latter happened, what the portal did was draining the magic items of magic to power itself, the magic items stopped working for a short time, when it came to charge-based magic items, they lost charges.
Another effect that could happen was that the user was shoved off as though he or she suffered a telekinesis effect.
Another possible effect was that the portal spilled either and inflict serious wounds or cure serious wounds out against the user.
Even when the portal sent somebody off, it could send somebody to a wrong place. However, about half the time, a portal worked properly and one could further stabilize it with a portal stabilization spell or by applying special portal.