The Spires

If you travel west from Ruvia, to the coast of Illegon, you will reach the sea.
If you look out to the sea, in the distance you will see a spire.
If you approach the spire in a vessel, you will see that it glows.
Ancient, made of stone and iron, four-sided it extends from the sea, it looks like it is midway through crumbling into the waters, held together only by that last frightful breath before the fall--the gasp of terror of a foot missing a stair in the dark.
What dwells within the spire is unknown. Certainly nobody who has ever ventured within has returned. The great seagates sometimes open for vessels when they approach, but those who enter never exit again.
A few brave adventurers have tried scaling the Spires, to find out the secrets within, but none* have returned. There is a small business of expert climbers in Ruvia, who specialize in getting foolhardy men up the side, though none dare to install permanent pullies or scaffolding to the spire.
*One man, a famous pirate called Iago of Jenoesa, who had entered the spire with twenty armed men, emerged from the spire alive after venturing in. He brought out with him a sack with half of his own weight in rubies and emeralds the size of goose eggs. His account of his time in the spire is obviously false--he tells a different one every time he is asked, and makes no pretense of truthfulness or consistency. It seems that his experience, and the loss of his companions, is too painful for him to recount to the public.
It is common knowledge that Iago of Jenoesa is no longer capable of sleeping.