Bruns took a few days to gather supplies, double-check his information, and ensure he had enough talismans. Then, he ventured into the sewers with the goal of first establishing a barrier at the border between the sewers and the tunnel leading into the Underworld.
The barrier would inform someone on the surface that an underworlder was passing through. It was a first alarm in case there was an attack or an underworlder tried to sneak away. There probably wasn't much they could do if the underworlder was sneaking away after hiding in the sewers or the city. But it would let them know the underworlders had been active.
And if the barrier sensed an underworlder entering the sewers from the Underworld, it would give the ones on the surface enough time to prepare for an attack or to catch the underworlder.
That wasn't the barrier's only purpose, however.
