The Wheel is the name that the Magisterium gives to the space created by the universe curving back on itself. While technically still part of the Bulk, the Wheel exists closed off from everything else. Inside this "bubble", a minor fluctuation in the Inflation caused completely different conditions to form.
The Wheel connects to every point in space. By entering the Wheel with just the right conditions, Magisterium spacecraft can go anywhere in the universe.
Flora & Fauna
Creatures of the wheel: nonsentient, self-replicating patterns.
Wheel beings: sentient patterns existing within the Wheel.
In the wheel exists a sea of exotic subatomic particles that appear nowhere else in all of the universe. Many of them have useful properties.