Disclaimer: UPG. My information comes from both personal experience as fae in both this, and previous lives, and talking to other fae (in Faerie) about it.
Disclaimer 2. Bold letters:
DO NOT step into a faerie ring without reading this WHOLE ARTICLE and understanding the Consequences. I disclaim all responsibility for your fate, desired or not.
The first thing to do is explain what a faerie ring is. It is a kind of planar bridge that allows two realms, in this case Earth and Faerie, to share a space, without allowing energy to permeate one another. This doesn’t mean all energy, but specifically mortal energy, and fae energy, the energies that are the fundamental part of the two realms. On the Earth side it is usually demarcated by mushrooms, flowers, vines, or other natural objects. On the Faerie side, it is demarcated by metals, plastic, and other unnatural objects. This is one (of the many) reasons the fae might take off with one of your items, as well. They are enchanted in such a way to redirect energy that would leave the ring back into the proper realm.
The field that the faerie ring covers is usually a perfect sphere, however if the ring is small it may just be a cylinder. The spherical faerie ring is usually used when an event is to take place on Faerie and Earth both at once. The cylinder is used when a portal between Faerie and Earth is required. Faerie rings that project spherical shields are also usually large, and often fae can be seen inside them from the mortal realm. The cylinder rings extend up about 8 feet on average, and the sphere fills the volume of the diameter, including underground.
In the times before, when fae and humans walked together in the same realms, faerie rings did not need to exist, and were rarely used, because magick was part of both worlds and it was not necessary to shield one from the other. However later, when it was time to withdraw, any sign of an area with high fae energy could easily be detected as a place where fae still resided on Earth. Additionally other factors (which may be described in another article) caused Earth’s natural magick to begin to fade, an effect that was highly undesirable to have spread to Faerie. So with the fae, went the influence of the Faerie realm with it.
However some fae of course, stayed behind, attached to parts of Earth by choice, obligation or compulsion. In order to allow contacts between realms, faerie rings are used. They are also used to hold events or rituals to be done by mortals and fae alike, things that still do happen to this day, typically by those with a relationship with the fae. Mortals of all types are typically “welcome” into a faerie ring, for better or worse for said mortal. It should also be noted that the size of the circle can be larger on one side than the other. That becomes immediately apparent when you walk into the ring. Sometimes, a faerie ring is as large as a courtyard or even castle or forest, on the faerie side.
Do note that if the natural objects enforcing the barrier of the faerie ring are removed or otherwise destroyed, the fae will quickly take down the whole circle. Take care should you choose to step inside. Now, to discuss one of the more interesting parts, the time disparity between the mortal realm and Faerie.
The time difference can actually vary wildly depending on where in Faerie you are, but is generally one year to one day. That is to say if you enter a faerie ring, every day you spend in it will be a year of time on Earth. There is an aging issue, on your return, because even though you’re in Faerie, temporally, you are still on Earth. You seem to disappear on Earth when this happens, but what has actually happened is you left the temporal frame of reference you were in when you entered the ring, and are now passing through time at (on average) 365.25 times the speed. You are still aging as this occurs.
Now when you visit Faerie in a dream, because only your spirit is going, it is the exact opposite. You are able to experience a third of a year of time on Faerie in only a night, and again it varies wildly, not only because of different time tempos in Faerie, but also because your spirit does not have to experience time linearly nor is it really bound to a certain temporal frame of reference. This is the same for most other planes however.
When you consciously (as in being awake) project to Faerie, you will experience time at the same scale as mortal time. As it would seem, the safest ways to experience Faerie is to dream your way there, or project your spirit there.
When you physically step into a faerie ring, you should understand that you are making a commitment to temporal acceleration. To bring the time scale in perspective, on average every second spent in the ring will translate to about 6 minutes in Earth time. If you plan on returning to your mortal body at any time, be absolutely short with your presence. Remember that you cannot predict the time of body failure, and while body degradation will occur slower (because it is actually doing less over time at the accelerated time scale), the first thing your physical body is liable to die from in a faerie ring, is thirst. So you can’t simply say your body will “age 10 years over 10 days” if you stay that long and assume you will emerge alive.
The easiest way to avoid this issue is to break the circle on the Faerie side of the ring. If you do this, you will start absorbing fae essence just from being in Faerie. This can be as simple as walking outside of it, to actually displacing or removing one of the objects enforcing it. In fact the sanctity of the faerie ring on the Faerie side is to prevent people who enter it from becoming fae, just from being present there. In general the fae will not prevent you from breaking the ring, because there really is no effect on them (the mortal realm does not start spilling into faerie because it is unbroken on Earth) and additionally, the fae rightly assume you know what you’re doing when you do this.
If you have spent more than a fortnight in the Faerie realm, do this, because on Earth, you’re probably already dead.
By now, you must have inferred the consequences to doing this. If you break the faerie ring, you will no longer be fully human, more equivalent to a changeling, when you return, if you can return. Once you have absorbed enough fae essence from Faerie that you are more fae than mortal, its over. You can return to Earth and look at it from the faerie ring, but will be unable to leave it. Have a nice wave goodbye.
One other pixie reminded me of something. If you eat any food over in Faerie, even within the ring, the process of becoming fae yourself will be accelerated. It doesn’t really matter how much. Once the food is digested, you’ll be too fae to return, in fact once it passes your heart on its way to your stomach, it has already started changing you. If you manage to get back to the mortal realm with Faerie food or drink in you, expect death not long afterward. The good news however, is that your spirit will return to Faerie.