Galahad gets an incling from his Deity, directing his thoughts to a history book he once read from before the fall of the world. It was about illegal activities that had been uncovered in the city.
Most smugglers went by sea, as it was easier. However, there are tails of an underground guild, the Xanathar Guild, who used underground tunnels and caverns. Little is known about the guild except they were thieves and slavers, and have been rumored to have been around for hundreds, if not thousands, of years.