The Vigil lives around a pair: a black hole and a star. The hole, Vesper, weighs 12 Suns. The star, Ember, is a quiet orange dwarf of 0.70 Suns, 1.5 AU away; the two go round each other every 188 days. Ember is too far out to feed the hole, so Vesper stays dark until the Vigil feeds it, and its own glow is far too faint to see.
Vesper's horizon has a radius of 30.4 km, small enough to drive across in about an hour. These pages explain the horizon and the effects of a black hole on light, clocks, bodies and orbits.
Where should I start?
Start with What is a black hole?. It covers the horizon, what size and density mean here, and why big holes are not dense.
The look of the hole comes next. Why the hole looks like that explains the dark shadow, the ring of bent light and the warped stars. Clocks near the horizon shows what happens to time for anyone trying to hold still, and why almost nobody can. Ships die of tides, not of curvature is the page about being torn apart, and why a larger hole is gentler than a smaller one.
Then the glow. Black holes glow is the page that makes the Vigil's cold economy make sense: Vesper's glow is 4.3 billionths of a kelvin, and it would take at most about 3.6 × 1070 years to evaporate.
Finally, the pair as a pair. A pair too wide to hear explains why the hole and the star will never merge and how the system was found by the star's wobble, and where you can live around a hole and a star explains why the Vigil lives where it does.
Where does it lead?
The glow leads into the heat strand, the horizon area leads into the limits strand through the memory a hole can hold, and the orbits lead into the voyage: how a seed was caught in the first place.