How is Ragnorak even possible?

The original Valhalla was on the Halo in Halo 3, Yet in Halo 4, Ragnorak (Valhalla) is a level in spartan ops…how?

I can understand it being possible in a War Games simulation, but how is it possible to even exist in the spartan ops universe?

None of the levels in previous Halos are canon.

Halo 4 is the only game with canon multiplayer.

two forerunner structures separated by a small hill, some caves and a river probably wouldnt be all that hard to find on a forerunner planet.

> two forerunner structures separated by a small hill, some caves and a river probably wouldnt be all that hard to find on a forerunner planet.

lol, true