The last twenty minutes of the drive saw the tunnel get wider. It turned from bare stone to stone interspersed with archways. Then into a single, consistent stone arch. In the last stretch, the masonry stopped, opening into a vast cavern. Sweets took a moment to shine a set of yellow lights upward.
Zipp opened the observation hatch, flapping rapidly up to touch the ceiling. “You look small from up here,” she called.
“It’s a nice temperature in here,” Sweets called up.
“Cool?” Zipp panted as she glided down. “Flying has definitely gotten harder since the last time I tried it.”
Sweets laughed a little.
“So this is the Blackstone chamber,” Marble announced in the cockpit. She pointed directly forwards where the blackstones bookended the cavern’s exit, “Point of no return.”
The two monoliths held enough space between them for three Capricorns to fit through. If together, the menhir would occupy a space equivalent to the Maretime Bay tram. They were embedded in the cavern’s rock face, seeming sharper, their shadows more distinct. Dark was not the right word to describe their intensity. Their onyx-obsidian color ate any light that was shone on them. When hit from the right angle however, they would refract light into spectra, casting back thin lines of red, orange, yellow, and green across the hull of the the Capricorn and into the eyes of its crew.
The lines moved like the reflections of street lamps as the mobile shelter approached in echoing silence.
Perhaps two hours of listening to the reverberated noise of the tracks had deafened the crew, or perhaps the brevity of the moment muted everything. A vibration grew taught, pulling the guts of every pony, sleeping or not, towards the opening between the stones. Afterwards, Sweets would swear that when they passed the threshold of the Blackstones, it was like flying as her guts dropped into her throat.
Zipp swore she saw the extension of the Blackstones a thousand times, extruded in perfect replication across a geometry she didn’t comprehend.
Marble knew the stones were but a shadow, and true comprehension was for only the truly gifted.
The rest of the crew felt themselves shift back, like falling from a dream.
And then, everything was normal. The chamber and the Stones were behind them, the tunnel was ahead and rising. The Capricorn’s rumbling tracks resurfaced.
“Phew, that is not easier the third time,” Zipp wiped a bead of sweat from her brow.
“It happens on the way back?” Sweets asked.
“It’s worse,” Z.Z. answered.
“I can’t believe I did that,” Sweets sighed.
“Hey look,” Marbles pointed. “Light at the end of the tunnel.”
Soon the stone masonry underneath treads gave way to rocky sediment. The sky opened between three peaks to the left and right. Sweets let Capricorn slow to park beside a tarn as she stared. Climbing to the observation deck, the Capricorn’s crew could see the tops of the rough cliffs of Unumbryo far to the south. Ahead, a lengthy series of hills and ridges led to the granite peaks of the Craterhold Basin. Austere green pastures and yellow weeds mingled between twisting outcroppings of granite. Only the vaguest impression of a road belied the vigorous civilization that had once controlled this now remote area of Equestria.
“Well,” Zipp clapped her hooves. “This is where our adventure begins!”