The Night has a thousand eyes, The Day but one

Let's explore a little more this idea of a world in which a day lasts a century.

Imagine the day slowly moving from East to West. In the areas that are light, plants would grow and animals flourish. In the areas that are dark, there would be ice and petrification. In the areas between - the "morning" and "evening" where the light strikes the globe at an angle, there would be drastic spring-like and autumnal changes. In the morning, we would find a world of thawing ice, rivers which have been frozen for 100 years suddenly breaking into motion, glacial flows, and everywhere green plant life emerging. In the evening, we would find the opposite: rivers and lakes freezing over, glaciers expanding, and plants slowly dying.

In such a world, if life could move, it generally would. Almost everything would be migratory and nomadic. The animals would gradually migrate from East to West to maintain the temperature and climate that was optimal for them - this would be unending. The only exceptions would be life forms equipped to live underground (who would largely ignore this slow waltz of the passing days) and those which were able to hibernate for a century.

The humans, who live in the day, would also primarily be migratory. I am picturing nomadic cities: huge trains of carts, caravans, and herd animals which would settle somewhere for a month or year and then move on with the day. Generally, the preference for advanced "civilized" societies would presumably to be remain somewhat to the West of the noon-line, to take advantage of the maximum fertility of plant life which had been exposed to the light for many decades. But I am also picturing entire civilizations founded on animal husbandry rather than agriculture: wildebeest and reindeer herders following the great migrations of those beasts.

In the morning and the evening we would find adventurers and pioneers - especially in the morning as new lands become exposed to warmth and light. People searching for new resources, new pathways, new lands to exploit. Adventurers in the evening would be outlaws and rogues, picking over the detritus left behind in the wake of the cities migrating Eastwards.

In the night live the orcs, and many other things. As evening advances they appear, like the vanguard of the darkness, hunting and raiding. In places, they might tangle with the rearguards of retreating human civilizations - just as, in the morning, human pioneers come across straggling orcs. In the dark places the orcs mine, build, and construct - citadels, tunnels and fortresses, which in the light of day human adventurers might explore.

Orc raiders and other night-time things would also be experts at concealment, though. During the night, they would burrow down into the earth, out of sight, and wait for decades if necessary for day to come so that they could emerge to wreak havoc. Then again, maybe both sides might engage in another sort of migration - from surface to underground and back again. Maybe both humans and orcs would have constructed huge city-states extending up from the surface and deep down into the crust of the world, so that during the day or night respectively they could ascend upwards or downwards as desired? Maybe down there great wars would be fought to try to undermine and destroy each other? Maybe just as the humans were coming to the surface in the light of day, the orcs would be concentrating their efforts on tunneling underneath their cities? And maybe all of this would connect with the vast and endless Underdark that lay deeper still.