You 'll probably know it already now, but I 'll tell it for other people who want to know this: You don't really need your heroes for this. just put your scouts and your army at one side of the island. start building a tower at the top circle at the other side of the island and wait in the lower circle till your builders are passing by.. select one and drag him into this circle. if he tries to escape, select him again and keep him in the circle. the moment the other builders reach the upper circle, the big chest will appear... that's all..