'Somewhere out in the middle of nowhere, a long time ago, the Chinese wiped out a tribe few people have heard of. Most of history is like this.' - Matthew White, in his book "Atrocitology"
Your party is standing somewhere. Where did you leave them? A lair? Village? Their own homebase?
What was there before them? No, before that. Before they were born. Before man was civilized. Before man was man.
There was something there. A being, a culture, a war.
If you were in Westeros, you could roll on this table and find out:
What stood here before you?
1. A village of the first men
2. A forest filled with horse-sized spiders
3. A cult of Children of the Forest
4. A battlefield of first men and Children of the Forest
5. A White Walker massacre
Or, if you were in the Everwood, my world, you could roll on this table to find out:
1. Tribe of Elephant Men
2. One of the ancient Druid circles
3. Giant the size of a skyscraper
4. Building site of a Moon elevator
5. Elves before they were cursed
6. Lonely witch with her archaic spells
Think about it. This is another thing to think about when your players are in a place. Any place.
What was there before? Make a table of the possibilities. Why? Because the more times you roll it, the more you have to think about it. Like say you're like me and you write "sentient elephant" on your table and you end up rolling it like six times in a row you might make up this Elephant Men thing and have a deeper understanding of your world.
I'm a firm believer in Stephen King's writing advice when he says that he doesn't make his stories, he discovers them. They are already in his head and he is excavating them. These random tables are a tool to help dig.
So do it. Come up with 6 things that were in your world before adventurers. Make them weird. Make them things you don't fully understand. Then roll every time your players go somewhere new. See what you dig up.