Players characters in my saga managed to explore and unearth most of the secrets of Calebais.
As they are from a Covenant dedicated to expand magic theory and integrate lost and exotic magics, they are very puzzled by the Hrools and the Veil of Mormulus, and they want to dig them.
The former one has some guidelines for its integration into hermetic magic theory.
How would you design the later one effect within Ars Magica rules?
I assume that, despite being Faerie, the Dryad is somehow a sort of genius loci. Hence, as a spiritual being, she can be bound using Spell Binding and Hermetic Empowerment (or maybe variations of these virtues, since Mormulus seems to have bargained with the dryad). It seems to me that the Veil is a sort of boundary ritual, and the dryad gives it energy so that it doesn't fail after a year. Also, the dryad kinda "manage" it, since she has some influence over who can pass or not, and she can change the password on request.
Obviously, the dryad is bound to the statue found in the upper levels.
Also, it seems realistic the veil was made possible through Faerie Magic.
Now, how would you design such a spell/enchantment? The Veil seems loosely based on the Rego Mentem spell "The Shrouded Glen", but it incorporates powerful Perdo Vim effects as well. What would you suggest?
There is many effects to consider:
The permanency of what looks like a Ritual is puzzling
Since it is affecting a target size of Boundary, it is a ritual... unless, somebody used Hermetic Architecture and then stacked various effect, including illusion & mentem effect, one effect preventing scrying (with a very high Penetration).
It is plausible, but it is a bit boring in term of discovery potential.
If it was a Spirit bound, should sustaining a Ritual not permanently drained is Magic Might (serf's parma) ? Thus after a while, the Spirit should dissipate and the effect collapse. However, what if there was a special technique which would allow to drain vis straight from an Aura to sustain permanently an effect ? Through Alchemical digestion, it is possible to kind of automate vis extraction - the magus still needs to keep an eye on the process. Could it be used as a base to have permanent effect ?
What I would propose is that an Aura can support enchantments as an invested device and her enchantment limit would be 5 times its Aura value. Does it require Hermetic Architecture ? I would be tempted to say yes considering that it is the only way to manipulate Aura.
Then, there is the effect itself, with this kind of labyrinth with a guardian. It definitely requires the presence of a Spirit of some form. It can a Ritual which transform a Spirit into a Genius loci. I am using loosely the word Spirit, as it could an entity from any of the three (four ?) Realms. The Realm's origin of the Spirit will dictate the form of protection granted to the area.
It is definitely a kind of unique ritual similar to the Ascension of a Daimon.
So other source of inspiration for a breakthrough could be the Mystery holding the secret of Hermetic Theurgy, Ascendency and Invoking the Pact.
Another way to look at it would be a special initiation of the Living Ghost: a magus would sacrifice is life to become the custodian (guardian) of his covenant. He would trade some ability of the Living Ghost (namely his identity and part of his free will) for the powers to protect his area. There was one magus who is said to sacrifice himself to boost the aura of Durenmar, so it would not be impossible that there is various ways for a magus to give his life for a final potent and unique effect, possibly breaking Hermetic limits.
Finally, another way to look at the effect of the Veil is that it looks similar of somebody following a path to cross regio boundary. Here I would go back to Hermetic Architecture as the base to manipulate Aura and regio. It is a unique effect blending ReVi effect with Imaginem/Mentem effect, probably based on "Closed Privacy of the Enchanted Regio". Maybe "One Path amongst a Myriad", Re(In,Mu)Vi(Im,Me,Te) 94, Pen +0, constant effect. R: Touch, D Always on, T: Boundary, Mystery Enchantment. The path to the Inner Regio is controlled by a powerful effect which brings the visitor through a series of tests designed at the creation of the effect. If the visitor succeed, he is allowed to cross to the next regio, otherwise, he can either backtrack or try again. The visitor is physically in a intermediate regio, where time pass normally for all purposes of aging, hunger, thirst and need to sleep.