The harbor is the first 'blue' zone north east of the City of Brass. You will need a boat or some other method of traversing water to go beyond the dashed lines on the map. 1,2, and 3 are all ladders you can go up or down to access the pier. The locations labeled 4 lead you to the next zone, the ocean. It's worth noting that you can also swim east of the leftmost 2 in order to go under the pier and access the ocean as well. The Prodigal Sorceror is found here at the square labeled (A). He carries a blue mana gem. (Note: this is a difficult to map zone and will be remapped it at a later date for clarity)