I have a world with 9 year days. That is, the day-night cycle here lasts 9 years, where ours lasts a mere 24 hours.
Very similar to a tidally locked planet, except the habitable belt moves. The species that have come to live on this planet have evolved to instinctively migrate west to avoid the night. The terrain consists of very few mountains and oceans, with lakes and vast expanses of plains being more common. Towards the poles, the night side temperatures become so cold that massive glaciers carve the land and provide water to fuel non-mountainous rivers. While the day side gets less water, the land itself is more hospitable.
The astronomical features of this world include a small ring system and multiple smaller moons.
As I was designing the cultures living in this world, a question began to arise. If these people are circumnavigating the globe since before they were even self aware, would the idea of a flat earth even start in the first place? If this world's inhabitants did once believe in a flat Earth, would their migratory nature allow them to discard this idea sooner?