The high, wild vastness of the Mountains of the Moon holds wondrous places far removed from the outside world, like closely guarded secrets the mountains themselves deliberately conceal from sight. In deep plunging valleys, hidden by impassible massifs on all sides, are things which would be famous throughout the world if somehow enough outsiders could visit for word to spread. As it is they sit mostly unvisited, unexplored, and unseen.
In the heart of one such valley, one of the most remote valleys of all, stands The Tree. It has no other name, for it does not need one. All who know of it know there is no other tree in the world like it, and no tree for which it could be mistaken. It is a Tree like no other.
The valley itself is a thickly-forested cleft gouged from the mountains by the blade of the river running through it. Rising up above the greenery around its feet - if "rising up" does the sight justice - the Tree stands, well over a mile high, as high as some of the peaks on either side of the vale, high enough for clouds to cling around its trunk and for its highest branches to be permanently coated with frost and snow. Its bark is covered with forests of moss and lichen; its roots spread beneath the surface of the world in a vast web which reaches beneath the mountains themselves; and its great bulk contains entire settlements, towns, kingdoms - bored into its trunk, nestled under its feet, or spread across its network of branches.
The Tree is mostly unvisited, unexplored, and unseen - but not entirely. Sometimes adventurers, traders, sages or exiles make their way to that distant and isolated valley because of a whispered rumour or indiscretion heard in some opium den or tea shop in the oligarchies or Sughd, or even the Yellow City far in the south. They come in search of riches, opportunities, or even simply to say that they have seen and climbed such a tree and lived to tell the tale. Many of them never leave. This book enables you to run a campaign in which the PCs are some such visitors to the Tree, and see if they can survive - or even thrive - in its mountain-high frame.
[I will be blogging somewhat less in future months, as I'm on a productivity drive which involves cutting out almost all non-essential internet use. If posting seems light, it's not because I've gone away, but because I'm focusing energies on concrete goals.]