Risen

Every time you complete a quest that is written about in your journal, it will count towards the total 250 needed for this achievement. As with similar achievements, the count is independent of your gamestate. This achievement is most easily done just playing through the game, and it will probably pop before you reach the end just by doing the quests given to you.

If you want to boost this along, find a couple easy quests, save your game, complete the quest and reload. Repeat completing the quest until this unlocks.