Individual Dungeons, aka Indy Dungeons aka Indies, are dungeons that are only accessible to players who use a key to access that dungeon and members of that player's party.
Individual Dungeons can be be accessed by using keys that can be obtained from NPC [Pointry], drop from other Individual Dungeons or bought on the Market. A certain minimum Main Characterlevel is required to in order to use a key. Once the dungeon is opened, an instance is created that is only accessible for a certain amount of time.
Individual Dungeons have cooldown (CD) periods, during which they are inaccessible (usually 20 hours). You can view your dungeon cool downs in your Character sheet (Alt+N) under the Dungeons tab.
Individual Dungeons are usually limited to a formation of 6 characters (Main Character + 5 Mercenaries). If a player has more than 5 mercenaries but does not manually disable at least 3 mercenaries when starting a battle in an Individual Dungeon, mercenaries will automatically be disabled at the start of each fight, starting with the lowest level mercenary and working up, until the limit is satisfied.
Warning: you have to stay inside the dungeon after killing all the monsters in it until you see the popup window telling you that you have completed the dungeon, or you will not receive the dungeon reward boxes.