Best free "open world" games

Open-world games give players the freedom to explore a game world with relatively few restrictions, letting them decide where to go and, often, how to approach the problems they encounter. Instead of following a strictly linear path from one objective to the next, you can wander off, discover hidden locations, tackle side quests, or simply get distracted by something interesting along the way. The formula is strongly associated with RPGs, but open-world design appears in plenty of other genres too, including action-adventures, shooters, survival games, and even platformers. The only real danger is setting out to complete one simple task and somehow spending three hours exploring everything except it.