The underpass is covered in rattlecan, the colors and layers ripe for an archaeological excavation revealing cultures and pigments in strata, year by year, decade by decade. There are masterpieces, and remains of them, commingled with lazy tags and later imitators, swaths of cement canvas painted over and over as part of the dueling rituals of generations of street-savvy artists.
No inch of the underpass is spared, neither walls nor pillars nor the concrete spillway that ran down the center, save a perfect radius surrounding a solid black circle.
Standing between the North-most pillar and the North wall of the underpass, back against the pillar and toes six feet from the wall, is inscribed in matte paint a black circle no larger than thirty centimeters in diameter, and surrounded by a perfect circle of clean concrete stretching a meter.
The surrounding art stops cleanly at the line, as if it had been masked off with a laser-cut stencil. The perfect line does not interrupt any designs or lines - instead, they look to have been designed around it, borders executed with precision.
When questioned, local graffiti writers know nothing about the strange marking or the border that surrounds it.
Across town, in a line due North as the crow flies, and at a distance that puts it just below the horizon from the first: a second black circle intrudes on a basketball court covered in sidewalk chalk.
It appears to be drawn with charcoal, and is the same size as the first. Childrens' scribbles swerve unnervingly away from it at the last moment, leaving a meter of blank pavement clean.
Due south, just over the horizon, in a cemetery dating to the 1800s, a single grave marker stands out from the rest - a bronze plaque with an acid-etched circle. Leaves do not settle around it.
Reaching out to touch the circles results in a horrible compulsion to pull away.
I decided to take choice out of the equation, and jump onto the chalk circle from a stepstool. When I awoke, I could see the stars regardless of daylight, and track the Moon through the Earth itself.