That led me to it's thematic predecessor, Wasteland. The third was Underlight, a new online world set in a dreamscape that may or may not be real. A few more titles have come to me since then, but the total is still pretty small. Start with a basic medieval or similar setting. Mix in some nice dark places to explore.
Dungeons are good.
So are caves. Next, add the usual character classes like knights, mages and rogues. Then stir in the usual mix of weapons, armor and potions. Season to taste with some magic. Don't forget to include Fireball.