I have two ideas for new achievements based on world exploration and it will encourage players to play in worlds or explore.

The first of these is the world explorer achievement.

You get this one in steps, much like other achievements for playing in a wide variety of worlds. It would have names like

traveler: 3 worlds
explorer: 10 worlds
wanderer: 25 worlds
trailblazer: 40 worlds
pathfinder: 60 worlds

and so on, though of course those names might need adjustment.

the second kind of world achievement is a mastery achievement, which a player earns for playing multiple games in the same world. These would not require much to name it would just be "X Y" where X is the title of the world and Y is the level reached on that world

for example

Cyberpunk novice 92 times)
Cyberpunk initiate (4 times)
cyberpunk adept (7 times)
Cyberpunk master (10 times)
cyberpunk grandmaster (15 times)

(numbers might need adjustment, as would names., though to make things simple and not put a strain on the team, the Y names would not change between worlds.