Swefnia is the Dwaian world of dreams. Every time someone goes to sleep and enters a dream on Dwaia, they enter this world, which is the same for everybody. People can meet eachother in Swefnia, and if they're good at remembering dreams, they can even have productive discussions while asleep. A Dwaian who is asleep can wake up in Swefnia, and a Swefnian is forced back to sleep when their Dwaian counterpart wakes up. When someone dies in Swefnia, they wake up on Dwaia, and they will become a different Swefnian when they go to sleep again. There is also evidence that, when a Dwaian dies, they wake up in the Swefnian realm, and eventally a new Dwaian is born who is connected to the Swefnian. Many Dwaians use this freedom to have crazy adventures in Swefnia that they would not dare have on Dwaia. Some people, however, use their Dwaian form as dispensable, and their Swefnian form as their base form.
At almost any point, there will be an overlord of Swefnia, called the Oneiros, who possesses nigh omnipotence over this realm. In order to become the Oneiros, one needs to find the current Oneiros inside of Swefnia, and tear a certain object called the Medallion from their heart. This kills the Swefnian self of the current Oneiros. Then, when one ingests the Medallion, they gain the powers of the last Oneiros.
Most accounts describe the Medallion as looking like a small piece of liver meat with a plastic-like but organic tag on it, in which an insect is encased. Progressive accounts seem to indicate that this insect grows every time a new Oneiros is assigned.
Swefnia experiences time distortions, where some regions experience significantly more time than others each night. In some regions, time moves faster than in Dwaia, and in others it moves more slowly. Because of this, some dreams can take centuries, while others may pass by in mere seconds. The Oneiros tends to construct their own time bubble where many millions of years can pass each night. This allows them to live in their own universe for eons, without having to worry about people with malicious intentions wandering in. As a result, the realm of Swefnia is usually not too strongly influenced by its Oneiros.
The lands of Dwaia seem to match up with the regions of Swefnia. Thus, it has not been possible to contact people from the other planes of Dwaia via Swefnia yet. Usually, when you move very far away from the place in Swefnia where you started your dream, you will be transported back to your original place around the time when you need to wake up. However, sometimes, the Swefnian manages to avoid the transportation, which causes the sleeping Dwaian to be transported to the place associated with the place the Swefnian goes to sleep. This can happen, for instance, if the Swefnian in question is the Oneiros.