The "tracking device" turned out to be a large disc with a chain attached, like a huge gaudy medallion. It wasn't operated as such; it relied on the holder entering a receptive state and then being able to sense what the device was indicating. Cersei was instructed in its use via the Receptive Telepathy spell, and once in the proper mindframe, she could sense that it was indicating a direction of strongly west-southwest. This meant their course led largely down the wide Senna River, but their destination most likely lay on the far bank.
So they rode their horses out of the Farm Gate and followed the curve of Tarak's wall to the south, to the Docks. There, a raft was secured, with a raftsman trusted by the Council to keep his mouth shut.
That's how the approaching dusk found the five of them, four passengers and the raft's captain, drifting steadily downstream, toward the middle of the wide channel, where it was safest. There were a few aquatic threats, but water travel was the least dangerous way to go since the coming of the Night Plague.
While all of them had been outside of Tarak, it had been a long time since any of the city dwellers had been this far away from the metropolis. Other than the burble of the water and the occasional nervous stamping of the horses tied to the raft's central post, the land was quiet compared to the constant underlying hum of the busy city. The river cut through the Vendall Valley, with the majestic high peaks of this part of the Toran Range rising all around. The truly impassible mountains were behind them, to the southeast, but they were still a long way from the simple foothills and floodplains that made up the central part of the Oresti region.
(yes, it's taken from shore, but it's not too hard to imagine the view from the middle of the river)
The raftsman, Vorman, was dozing at his stool at the raft's rudder and propeller assembley (a specially-shaped Ever-Turning Wheel mounted on a moveable armature near the rudder provided extra thrust as well as a way to travel upstream). Vorman wore travel jewelry, which eliminated his need for food or water and cut his need for sleep to merely two hours a day, but he seemed to take those two hours in a thousand catnaps over the course of the voyage. His reputation for keeping his mouth shut applied to his traveling chatter; other than the basic raft safety instructions and the occasional request ("could you stand over there," or "let me know if you see anything along the left bank," for example), he kept to himself, and seemed almost bored.
As night fell, and Vorman was at the far end of the raft, it was a good opportunity for the group to talk privately about the full nature of the mission and what might be called for.
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