Back when I was a MUD coder, I implemented a neat 'exploration' mechanic: the game kept track of where the characters had been, and displayed it as '% of world

Back when I was a MUD coder, I implemented a neat 'exploration' mechanic: the game kept track of where the characters had been, and displayed it as '% of world explored', which a lot of players had fun trying to get as high as they could. If one wanted, one could further incentivize exploration by actually tying such a '% of world explored' stat to hack-n-slash gameplay.