The Forbidden Oasis (The Forbidden Oasis) is a medium-sized location of the game and one of its features is that it is optional to explore it. This means that visiting the Oasis is not required to push the storyline forward. Personally, I recommend against skipping it, because you can get new quests here and find many valuable items. Still, you need to keep in mind that access to some of the areas within the location may be difficult, or restricted, at first, as a result of too low an experience level of your party, or to few shards (to learn more, see further into the text).
The way to unlock this location: On the war map, pick the "Investigate the Shards" operation, which becomes available after you have obtained any of the shards in one of the remaining locations, in the game world. Complete this operation, by spending 4 Power Points.
Recommended experience: It is best to explore the Oasis to its fullest after you have progressed to, at least, level 12, because there are many monsters here, around rifts, and spiders in the South-Eastern cave. Even stronger monsters can be encountered in the chambers of the temple, although you can always retreat from there and return later into the game.
1) The Forbidden Oasis is a location of multiple levels and it takes some time, before you master traveling between the individual levels. First of all, search for various paths on the brims of the oasis (especially in its Eastern part). What also helps, while moving between the individual levels, are narrow cave tunnels, but it is easy to get lost there. Apart from that, search for ladders and spots, where mages can use their unique abilities, e.g. to complete a bridge. Also, watch out for the spots where you can drop from a height - if you want to reach a lower level quickly, consider summoning your mount.
2) While exploring the Oasis, You do not find too many unique places. The exception is the Solasan Temple, which is connected to several side quests. If you want to access the temple and its successive chambers, you need to have shards on you. Just to remind you, you obtain shards by using ocularums in various areas of the game world. To access all of the chambers in the temple, you really need to have lots of them on you so, you are bound to return here, at least, several times. As an aside, it is very profitable because, apart from experience, Power Points and Influence, you also obtain many valuable items.