The Third Tower

Dwarf Towers start at the bottom of the crust of the planet. They would go further, but there be monsters down there, that lurk in the caves and the fire. They stretch from the bottom of the crust to higher than most mountains, all stone removed from the base built up around the top until they run out.

The tallest (and the first) of which was so tall that no one can go. It's so high that all water freezes, all breath ceases. A garden was built on the top, but the spell holding it failed, and everything flash-froze.

Queen Mab has preserved it, and if anyone else could see it, it would be a marvel to behold.
I do not know where it is, but I know it was the third one built. Might put it on the North Pole.

Type

Tower