I recently decided that I want to make an adventure map with a friend, but we don't know where to start. Almost every idea has been taken and we do not want to reuse those ideas (such as the whole, "Evil AI" theme). We also do not know what kind of map we should build on (Generated, Flatmap or Custom Terrain).
So we wanted to ask you adventure map makers out there, where do you start? How do you plan and what kinds of features should an adventure map have?