OPO1, or Outer Plane Object 1, is a spherical world, with gravity pulling towards the center and it is inhabitable on the outside. Estimates suggest a surface consisting of 78% deep ocean, 5% shallow seas and lakes and 17% land. A layer of atmosphere of around 10 km covers the surface composed mainly of elements 7, 8 and 18. The Inner Plane is connected, through thousands of portals, to locations mainly on the land surface of OPO1, with a few in the ocean and even fewer high above the surface.
Life inhabits the thin layer of the surface in four major forms: bacterial, plant, fungi and animal, all with the exception of the plant forms bear resemblance to the lifeforms of the Inner Plane. Sapience is encountered in the animal forms as the primate species human and ogrid and the archaosaur species drako.
Within the geographical region centered on the Inner Sea, great advances in the technology and culture of the species human have been underway in the last hundreds of cycles. The spread of metal working has enabled the use of stationary agriculture for subsistence and with it, the construction of large settlements. To the north of the Inner Sea, society is still organized around tribal lines, while to the south, it revolves around a caste system of slaves and freemen. Between these there exist a number of civilizations in the midst of transition from the tribal to the slave system.
Boundary Walkers can visit OPO1 only by merging with the conscience of a human. This merging can take the form of cooperation between the two individuals or of the complete subjugation of the human by the Boundary Walker. Countless explorers, scientists, exiles and institutional agents thus live on OPO1, offering the species there the powers of Thaumaturgy, element manipulation, mind alteration, but probably the most important - knowledge.