So are we agreed on the "shape" of the covenant?
I propose the following description. Let me know if you are in agreement by liking this post.
The magus, when he first discovered the valley, initiated the construction of a manor house at the spot where the aura was strongest, adjacent to a small waterfall. Construction continued over the years, expanding the manor house with additional structures for the mundanes who lived there permanently, but also room for additional magi for a future covenant.
But then, before construction was finished, the magus suffered from an experience that affected his mind permanently (perhaps Twilight). It made him confused over the overall plan. He had the workers stop some of the work, adding differents wings or buildings that sometimes made little sense, tear down parts of the structure and add some independent buildings with no apparent purpose, as well as create decorative elements that clashed with each other.
The result is a fairly chaotic collection of buildings centered around a manor house that sprawls out in erratic ways, with a confusing floor plan. Corridors that circle around a room to reach its door, a flight of stairs that lead nowhere, a half-finished square tower, columns, terraces and gardens (that are either bare or growing unchecked) are all elements of the structure. With so few mundanes present, an ever-changing focus to their work and the absence of full-time occupants, certain parts of the covenant have fallen into disrepair.
There is a magical oak tree of huge proportions growing in the valley, lumpy and twisted. The magical aura is strong there, but strangely enough this is not where it is strongest. That occurs about sixty paces away, near the waterfall. A narrow opening in the cliff face lead to a large cave (the opening is now inside the manor house). There are a few tunnels leading to secondary caves, but one does not notice them immediately.
For on the jumbled rocks to one side of the cave is a something completely incongruous - a Roman galley, broken in half. Wrapped around it is a petrified sea serpent, its body as thick as a man is tall and its head raised in a soundless roar.