Marelantis

Ancient texts affirm that on the night of a great storm, the city of Marelantis disappeared beneath the waters of the ocean.  While most believe this story is an old-pony-tale retold each generation to spark the imaginations of foals, a few relics have surfaced over the years and been hoarded away by those who hold out hope that if enough clues are collected, the location of this mysterious city may be calculated.  Almost nothing is known about the inhabitants of the city though some less-than-reputable sources have been found that say that the town was full of powerful Unicorns who had learned how to enchant stones with a spell that caused the stone to gain the ability to augment the magical abilities of the pony holding it.  Rumors abound that they were able to create fantastic machines that used magic to carry ponies into the sky or under the water though unlike the stones, no objects of this description have ever been located so these rumors are generally disregarded.