Maybe thinking about the exploration in your game as a point crawl could serve you well.
Think up a bunch of interesting locations and encounters for your players to experience, then for each encounter/location roll 1d4-1, that is how many other encounters it links to, randomly pick from your other encounters/locations for each link.
For how to generate the encounters/locations there are many tool sets to draw ideas from. Books like the Tome of Adventure Design, Worlds Without Number, Knave, Shadowdark, etc. Online tools from don jon, hexroll, or others.
Let me know if you would like other specific recommendations and happy gaming!