Magnet Hill

Well the answer to the question of Magnet Hill's creation is quite simple: After Fourside was built, the huge metal skyscrapers attracted the magnets that were created naturally underground. As more and more buildings were built, the magnets came closer and closer to the surface until they were exposed. Then the sewer system was built underneath. Also, there's a wall around it because people were complaining about walking past it and having their credit cards erased.