Covenant Lands and Environs
Kyiv
The city of Kyiv lies slightly downstream and across the river from the covenant. Mythic Kyiv has seen better days, yet remains a vital city that dwarfs London in size, though significantly smaller than Paris. It is situated on forested hills, and wood is by far the dominant building material, used to pave roads and build fortifications, very little of which is of stone. Its ironworking is not nearly up to the standard of western cities, let alone Saracen lands. But it is a mistake to consider this a primitive outpost on the edge of civilization. Kyiv is a wealthy city, with churches and schools and bustling craftspeople and merchants, though it lacks a university.
Kyiv is a cosmopolitan city, with a large Jewish population, some Muslims and even some pagans, though these are persecuted if they bring notice to themselves, and may not worship. Rus is wealthy, and money changes hands. You can find virtually any kind of person here, Varangians from Britain and Scandinavia, Saracens, Venetians, "Romans," steppe barbarians, Saracens, Jews and sometimes even people from mythic lands further afield.
The modern concept of Russia does not exist yet. This is one of the most tolerant places in Mythic Europe. The Rus have not yet been sundered from Europe by Mongol invasion (and this might never happen); their nobility is linked to that of Christendom by ties of blood and marriage. Barbarian Cuman raiding and settlement to the south of Kyiv and the decline of Constantinople since the mid-11C have sapped the commercial vitality of the city, but not entirely.
The Rus' have largely been Christianized by this time, yet many pagans remain, finding ways to continue observing the old ways. Especially in the countryside, people often prefer to adopt both Christian and pagan ways. Kyiv itself is mostly Christian.
The covenant ought to be clearly visible from Kyiv, its sculpted terraces and embankments, yet one's glance usually slides right past it uncomfortably.
The Dnieper River
Kyiv is situated on the west bank of this vast, vast but usually sluggish river that dwarfs the Rhine in size. The covenant is situated on the east bank.
The Dnieper freezes over most years during Winter. Between Kyiv and its terminus at the Black Sea lie seven rapids around which boats must be portaged and raiders waiting to attack commerce at its most vulnerable. On the other side of the Black Sea lies Constantinople, gateway to the Mediterranean.
The city of Smolensk, far to the north along the river, is a point of portage that eventually allows access to the Baltic, or to Novgorod and the northern interior.
The lands of the Rus
The lands of the Rus boast hundreds of urban centers, yet are vast beyond the imagination of most Europeans, abysses of unspoiled territory large enough to swallow entire realms. Men being what they are, all of this land is claimed by one ruler or another, yet the land yet belongs to itself. Magi in the west often feel threatened by the encroachment of the Dominion, but not here, where myth meets mundane, where the faerie gods of old have not been fully supplanted by the new order, and even where people have never sojourned in sufficient to recast the primordial magic of the land in their own image.
A man can get lost in the wonder of these fantastic lands and never return.
Politically, the Rus have fragmented into warring states. Kyiv has been repeatedly sacked by her rivals and is no longer even the nominal capital. To the south, Pecheneg and Cuman barbarians roam unchecked.
Parum Sanctus Bellum
The covenant lies within an uncomfortably strong Magic Aura, vividly sharp and alive, attuned to ancient powers alien to, perhaps alienated by humanity. The sun is hotter here, the winter sharper, the flowers sweeter, the decay where land meets water more sickeningly sweet. This is a beautiful place in its own way, but a perilous and untamed beauty.
This has not stopped magi from yoking the land to their own intentions.
The main site of the covenant is entirely artificial, a doubly-terraced plateau that rises from the low-lying shore of the river, held by massive retaining walls of unbroken rammed earth that to the unpracticed eye seems a natural, albeit unlikely, formation. But a magus would immediately recognize that this work has been done magically, probably by Rego Terram crafting magic.
Most of the covenfolk live on the first terrace. The magi all live on the second.
The Great Hall lies in the center of the green commons at the center of the covenant. This domed building of wood and plaster has a large central chamber, for which it is named. There are always at least two covenfolk awake here to serve magi. It is a place where magi can talk, or read notes left by other magi on break during their odd lab routines. (And all magi have odd routines; after all, do you really want to do critical work on Perdo Ignem during the day? Or Creo Corpus during an hour overly dominated by Saturn? Or read a book about Herbam during the 11th hour if your name corresponds to the number 426 and it is spring? Of course not.) The covenant's Charter has been rendered on the wall opposite the door of the main chamber in large Greek, Latin and Hebrew script, side by side, with exact but enlarged duplicates of the member's signatures. (Please don't count, as the number of PCs may change.) Your signature is there, as is that of Telemachos, whom you have never met. Beneath each signature is the location of his land. The other walls are not decorated, though you may change that.
The Great Hall has a kitchen and heat but no fire. Various enchantments prevent any fire from burning in this building while maintaining a comfortable temperature year-round. Eirik sleeps in a small room that doubles as his office.
Beneath the Great Hall, larders and storerooms have been delved into the earth. The library is also here, though the covenfolk implore magi to use the catalog and not to enter, because the librarian beats them if they fail to convince the magi otherwise. The librarian is a dour fellow who never leaves the library, hates to open the door, and hates light. Given a choice, he prefers to deliver and receive texts through a small hole in the wall with two sliding doors. But if a magus insists on viewing the library and promises to do so in total darkness, the librarian will admit him but not otherwise, and will lecture the magus deferentially but definitely about the evils of light and moisture. The librarian has an iron collar about his neck (if you manage to sense such things) and smells of onions. If you manage to see the library in the dark, it looks pretty ordinary.
One vast subterranean room contains the covenant's scriptorium, which is completely strange. A small viking boat is suspended from the ceiling. The dragon prow has been replaced by a rostrum from which a hortator in the Roman fashion beats a steady pace. A viking warrior is chained to each rowing position, but sits at a writing table instead of an oar. With each beat, each viking etches a single line or feature onto the parchment or vellum he is working on, and redips his quill in ink. A boy scurries to and fro refilling the inkwells. A magus who looks closely enough will quickly realize that none of the rowers or even the hortator is quite human. Each is bound in iron, the rowers with a leg shackle; the boy and hortator with a collar. They exhibit a range of bestial features that one might construe as demonic, as perhaps they are. None of them speak. Eirik is either not willing or able to speak about them beyond, "rowers on a sea of ink; Telemachos bound them while I was elsewhere," but will be glad to let a magus investigate them—if the magus is wiling to first demonstrate that he has the ability and intention to take up the slack of copying texts, should he disrupt the work.
I haven't decided if the there are subterranean corridors that link up the magi's houses to each other and the Great Hall (nice during the winter), or the extent of the rooms delved into the artificial plateau. I'm open to ideas. 
Telemachos has a standing request not to be disturbed because he is "busy working on a tricky problem and would hate to have to start over." His note seems confident that he will be finished in no more than two centuries.
Without the use of magic, the covenant is not defensible against a determined assault, even from the river but especially from the east. The retaining walls are strong and of moderate height, even the first terrace offers a commanding view, but there are no flanking towers, and the plateau is too large to easily defend. Fortunately, the site defends itself from mundane observation, as previously described, and magi are not limited to mundane defenses should the need arise.
Demographics are deliberately left blank. Regardless of how many PCs show up, the covenant seems too large, too many buildings for covenfolk and too many sancta for magi.
How the covenant earns its keep is also left ambiguous at present. Presumably, some covenfolk trade in Kiev, or trap furs, or something like that. Covenfolk also harvest vis.
Some of the rest of this information might need to be fleshed out further. Covenfolk will be created as necessary. If you want to create a grog-level coven-person, write a one-paragraph description of a mundane Russian or Varangian or something like that.
Note that we are not using the "Covenants" economy rules. There's an entire city of resources just across the river, and the optimizations to improve a covenant's economy based on the rules do not always make sense.