Then you travel south for three days and you will arrive at the battlements of Cantra. The inhabitants are warm and friendly, although difficult to understand.
Every day the residents change the language. Each evening they forget the language that they used that day. When they awake they have no concept of language and communication. By mid-morning, they can grasp this concept and can communicate with one another using simple signs. By noon, a moderately complex language has developed. By mid afternoon, scholars and writers have written hundreds of books in that language they are using for that day, unfortunately, this books will be unintelligible to them forever. By evening the residents are asleep and the process is ready to begin again.
In the center of the city a large building houses a giant book that contains the history of the city in every language ever used in Cantra. Hundreds of scholars spend their entire lives trying to decipher the languages used on previous days in Cantra.
If you decide to travel to Cantra, arrive early in the morning, forget everything you know, and bring only signs.