Endless Paths of Od Nua is the vastest network of dungeons, in Pillars of Eternity. In total, ther are, as many as, fifteen levels to explore. At each of the levels, you bothare going to fight monsters and find treasures. Apart from that, there is an option to complete a number of side quests.
The dungeons are under the Caed Nua Stronghold (the map M13) and you can access them by climbing down the stairs in the Stronghold's dungeons (M13,7). A very important piece of information is that it is optional to do the full exploration of the Endless Paths. If you are not interested in exploring the location, you can restrict yourself to partial exploration of the first level. The purpose of this is to complete The Old Watcher main quest, by defeating Maerwald in direct battle.
If you want to explore the entire of the Endless Paths of Od Nua, you do not need to do that in one take. It is best to distribute the process over time and resurface, each time after you explore several levels, to replenish your supplies, and to rest (there are stairs on each level, thanks to which you can make the entire process faster). This is especially recommended, since there are strong monsters, on the lower levels, which you will fail to, most probably, with an underdeveloped party. Therefore, it is best to explore the lowest levels towards the end of the game, when your party is strong enough.
On the following pages, you find walkthroughs for all the levels of the Endless Paths. Descriptions of all the levels have been provided with maps, which you can consult to find treasures, hidden passages, traps or dens of stronger monsters.
Important information - While exploring some of the lower levels of the Endless Paths of Od Nua your team may encounter friendly beings. The only way to communicate with them is if you already know the engwithan language. The only way to learn this language is to participate in the Undying Heritage main quest during your visit to Defiance Bay (II act of the campaign). It's recommended that you wait until you've learned the ancient language so you won't miss out on anything interesting in Od Nua.