If i thought i was replying to someone who would every return to the world, this flame would cease it's flickering. But since no one has returned from these depths alive, if what I've heard is true, I will answer you without fear of infamy.
Sta come torre ferma, che non crolla
Giammai la cima per soffiar de' venti.
Be steadfast as a tower that doth not bend its stately summit to the tempest's shock.
And here Dante describes an evidently spherical world... "The lamp of the world [the sun] rises to mortals through different passages; but through that which joins four circles with three crosses [the position of the rising sun at the vernal equinox] it issues with a better course and conjoined with better stars, and tempers and stamps the wax of the world more after its own fashion. Although such an outlet had made morning there and evening here, and all the hemisphere there was bright, and the other dark..."
As the geometer intently seeks to square the circle, but he cannot reach, through thought on thought, the principle he needs, so I searched that strange sight.
Through me the way into the suffering city, Through me the way to the eternal pain, Through me the way that runs among the lost. Justice urged on my high artificer; My maker was divine authority, The highest wisdom, and the primal love. Before me nothing but eternal things were made, And I endure eternally. Abandon every hope, ye who enter here.