Well the game the legend of Zelda lets you play as 1 single adventurer, but there is a full world with many interesting races, cool magic, cool magical items, many dungeons (with bosses traps and puzzles) and many different enemies.
There often is a story about groups of people being a secret (good) organization. Also there is a spinoff of the zelda games where you can play not just as Link but as different characters and fight with them through monster hordes.
You could definitly make a D&D like game in that setting, not playing the hero link, but playing some "normal" adventurers, when Link is not there etc.