Go to the "lore" tab. There, you can write some lore. Play my game for a while, see what lore fits (if you want).
Or you can make bosses. Bosses have like a short novel in backstory. You can read my rough draft of Heart of Obsidion if you want. (it's not done).
Or if you really want to, you can make some dungeons. Scroll down to my dungeons part if you want some inspiration (only the bad one is complete. Don't touch my current rough draft for the good one; that's inspired on my friend that tragically moved away).
The problem with dungeons, and with all of it, really, is that I'm planning to do a marathon. I want a very high number of bosses, each with very good backlore. And same with dungeons.
But you can do the amount that you want, obviously. I'm not asking you to do anything- in fact, whatever you do I will be eternally grateful, even if it is just writing 4 words :)