Terra Ultra

Terra Ultra is a tidally locked planet with one side always facing the star and the other always staying away from the star. It has three moons that occasionally pass in front of the star causing a red moon phenomenon that lasts for 6 hours. The time between the red moons is called a month. Another phenomenon called Dark Ash happens when a bigger planet passes in front of the star causing a period of dark on the surface that lasts several months. No crops grow in that time and the temperatures drop significantly. In addition to that, there is falling ash that is known to cause strange diseases if it reaches the lungs. The cause is unknown but it is probably some strange creature that lives on the dark side all year and migrates to the light side when the planet passes in front of the star. The period between Dark Ashes is a year meaning 21 months.   1 day - 34 hours + 6 hours (night) 1 week - 6 days, 1 month - 5 weeks (30 days), 1 year - 21 months: 17 light + 3 Dark Ash (can vary between 2 and 5)   Despite the harsh conditions and extremely dangerous creatures that roam the wilderness of Terra Ultra, humanity managed to survive here by using the technologies of the first colonists to build great walls to protect themselves from the dangers of the outside world. The Fortresses are mostly built within a few km of a sea or a river to facilitate transport of goods and people. Transports on land are nonexistent and expeditions outside the fortresses are extremely rare because of the dangerous creatures that threaten them. Contact with far away fortresses is minimal to nonexistent and most trade is made with close neighboring fortresses. The places far from the sea are significantly less fertile and require food to be brought to them by foreign merchants while the local merchants go to the places close to sea to sell their resources that are significantly harder to find there. In essence, trade plays a big part in this world despite the highly dangerous outside area.