What Came Before?

It's a good idea to create a setting that isn't static.  Not only does a setting need to change as a game progresses, but it's good for it to have a rich and diverse past.  Not all of it needs to be explained to players whenever they stumble across some ancient mystery, but be sure not to allow each and every new discovery sidetrack what is happening in the present.  It is worthwhile to let players know that just because they find a cave painting in a cavern they are exploring, it is not necessarily a clue to the particular adventure they are currently undertaking.  The following videos provide some inspiration for starting points in creation of a setting with a past.