CoreWorld is a hollow ball at the center of the Earth, about one thousand miles in diameter, giving it an internal 'equator' some three thousand miles around. Gravity pulls outward, against the walls. Therefore, there is no 'ceiling'. Forests, deserts, cities, etc rise up and overhead in eerie, otherworldy perspective. In other words, a city fifteen hundred miles away would appear to be directly overhead, a thousand miles straight up.