I am working with the presumption that most magi aspire to having a stone tower in a magic aura, as their preferred Sancta. Or at least certain NPC Magi.
And that most mundane Lords will have a dim view of fortifications that aren't under their control. How does a magus in a tower avoid the pesky attention and ire of mundanes?
Presumably by making the tower look like something else - either invisible or an illusion or something not threatening (eg a tall pine tree)
Enchanting the entire tower is impractical, rather enchanted object that affects Target Structure, Duration Sun, 2 uses per day, triggered dawn & dusk.
But which is better?
Invisible still casts a shadow, and birds will fly into it.
Illusion of a tree will be static, but affected by lighting or wind.
I have no idea why any sensible magus would want a stone tower to live in. They are not very practical.
Best way of hiding it should be something along the lines of the spell The Shrouded Glen
Presuming it is not in a fairly remote location ...
Disguise it as a ruin. Or a rocky outcropping.
For some locations, cloak it with a variety of mists, fogs, and clouds.
Circle it with a labyrinth of thorny hedges or boggy moors, and the only path seems to always lead away from the tower. Decorate the area with vine-twined skulls. Haunt it with actual ghosts. (This may attract overly romantic would-be heroes.)
Circulate rumors that the place is cursed, and that any man not a virgin who sets foot in the tower will be struck with impotence. (This may attract certain non-romantic men. Or women.)
Put it, if possible, on an actual mountain top, high enough to be difficult to march on.
In short make it a dangerous nuisance to investigate or threaten, and don't give a reason to put effort into it.
First question is why they want a tower- a tower can be easilly hidden in a valley, but may be of more use on a mountaintop. tower in the city might go unnoticed on it own (in Pisa for example, where the leaning tower was just one of a set of period buildings). It can be made to look like some other kind of tower- lighthouse or signal tower for example, especially if a ruin. Also just because a tower is stone does not mean it has to look like a fortification- a stargazer's tower for example, might seem very non threatening.
My favourite solution is to hide it underground. Invent your own version of Conjuring the Mystic Tower that creates a underground complex. Then you just need to hide the entrance which is much less of a hassle than hiding an entire multi story tower.
Make it look like a tower that is clearly not a fortification. Made of wood, with plenty of apparent openings/open platforms for sky-gazing, aeries for birds, etc. You know, the kind of eccentric abode wizards live in.
This can be reality, just an illusion (hiding the actual nature of the structure), or misleading reality augmented with magic (wood and windows as strong as stone while the defenses look like something else).
You could conjure a butte/mesa/outcrop and put buildings on top of it.
You could conjure a very tall forest around the tower to obscure it from observers.
You could conjure a squat, wide building (like a roman villa) and use the stone more efficiently (towers suck except for getting a high view).
and getting a bonus to aurum labs or hermetic prestige.
Auram lab? I don't think there's been such a thing since perhaps the 1st edition.
Not that lab specializations were a thing back then as I recall.
See the Elevated free lab structure virtue. It provides +1 to Aesthetics and +1 to Auram Specialization.
I'm aware of Elevated. It does not provide any advantage to lab totals involving gold...
if you want to get literal auram means cool, auras means air, but AM Latin is more of a Latin light, which makes being snarky about a typo really just... yeah.
We all make typos. I know I've forgotten to type entire words on this very forum. But!
As it happens, I find that one particular typo particularly egregious. Because the sentence still makes sense. Which makes it extra confusing for those of us with a less than perfect command of the language.
Probably because finding and building a place to form a covenant is a problem that many magi face, and there is a canon spell that speeds things up quite a bit by building a tower. Also Durenmar have towers, and that probably make it look fancy to other magi, even sensible ones!
Back to the OP, maybe that's why regios are so prized! Find one and build your tower in an upper regio level, unseen from the mundane world.
And when you locate a lacunae 70 feet in the air above a city how else are you going to reach it?
Right. A floating house would attract attention!
Towers have a small footprint and some magic auras aren't very big, and overall the Aegis of the Hearth isn't very big either. Personally, two of the sagas I've played in we've just created wider but shorter buildings because it's just more practical, especially given how Conjure the Mystic Tower doesn't give you 'standard' sized labs once you take account of how walls and stairs will eat up your square footage.
The only reason to use Conjure the Mystic Tower is tradition. It only uses about 11% of its potential production if you do not count the empty space (which is how other Creo spells work) and even if you count it as a solid block of stone there is unused material. It is a legacy spell at its level, which is the only reason for its existence, that with minimal shaving you could get to level 30.
Without changing the level, you could produce a version of it that has something like 8 towers connected by a thin stone ring or a large fortified villa with 4 towers and stables. A level 40 version would produce a large sprawling castle with more towers than you could use in an average Covenant or a whole large town with walls, workshops, and warehouses. A level 45 version could produce Rome or Constantinople.
If it does not show, I rather dislike CtMT as it is presented in 5th edition. While I have no issue in general with inefficient spells, CtMT is an extreme example of one.
EDIT: In line with the thread, the two alternate versions of it I presented could be concealed and not come across as fortifications. The 8 towers in a ring could easily be made to look like a monolith, like a small Stonehenge. For the villa you could make the towers into post mills or tower mills, which became popular in Europe in the 11th and 12 century respectfully. While they could individually be partially or fully functional (a Magi could use one for motive power in his lab), a villa with several of them in the middle of a large cropland would appear as the estate of a wealthy farmer rather than a military instillation.
Preach. I've certainly never used it, I always redesigned - once for a Verditus forge and once for a Roman villa (though that was mostly craft magic). Another person in our group designed an iron version of the tower. And once I used a giant conjured calabash gourd as a basis for a small tower.
Honestly you could conjure a giant rock with some rooms inside and it would turn out better than Conjure the Mystic Tower and be less conspicuous.
OTOH with the rules regarding craft magic it is an entirely impossible spell to pull off since it would require an outrageously high finesse score.