Pathfinder game system, what you need to know is that it's based on the core rules of Dungeons & Dragons 3rd Edition. Needless to say, dungeons feature pretty heavily in the tabletop game. So Pathfinder Online has presented itself with a bit of a conundrum: How can it combine the traditionally instanced format of MMO dungeons with the open-world approach of the game? As detailed in the latest development blog, the team is aiming at something between the normal instancing methodology and more sandbox-style open regions.
In short, while dungeons themselves won't be instanced, the entrances will be hidden in various locations. When a dungeon is generated, a player who finds the entrance will have that dungeon locked to him or her until the dungeon is cleared, at which point it will despawn and be replaced by another dungeon. It's an interesting idea, and it's well worth reading the full blog for a look at how this system might work in practice.