When you see "There is treasure in this city", you should mouse around the outskirts of the city that you are visiting. Somewhere beyond the city "limits" you should find a chest. Click on the chest and you will be given a reward. The rewards can be a relic or spell or a KP. It is just a nice little bonus. My experience has been that you only get three chests per day...maybe others have a different experience. In the time that I have been playing, I have never received a coin in the chest...just relics, spells, or KPs. The location of the chest generally varies from city to city and also from day to day...again, from my experience. Hope that helps!