Storyteller's note: This post will attempt to put what information has been gathered thus far in context (here: what is known by Onkel Smit and Master Arachnidus). As with the previous connect-the-dots posts, little or no new information will be presented.
The Ordo Ultima Thule has had a base on the dark side of the moon for at least 25 years. It is believed that this is the logistical and command centre of the Thulist activity on Argos. Nattland lies in the Crater of Yogoth, deep in the Ocean of Despondency. The crater measures about 36 furlongs across, its walls reaching up to about 2,300 feet from the crater floor, and some 1,000 feet above the external surface. Six fortresses line the crater's edge, among them Tower Helreginn. Situated on a lofty peak South West on the rim, this tall tower is assumed to be the heart of the moon-base.
The actual function of Nattland, whether it be supply, troop- and/or fleet-base, research, or perhaps even a colony, is not known. Still, that the base represents an important anchor-head for the outsiders is beyond doubt.
East in the crater lies what appears to be a town or larger settlement, and a rudimentary analysis suggests that it can house somewhere between 4,000 and 6,000 people. Apart from this, the other installation large enough to house a significant number is the fortress guarding the pass allowing entry to the crater from the North. The crater's floor is criss-crossed by roads that allow access to the various sites and installations, and Reavers patrol incessantly above the lifeless landscape.
Scouting of the area has so far not revealed any natural occurrence of neither water nor vegetation. While the Thulist civilization is well adapted to living in constructs deep in the void, according to the Commonwealth, they are to a certain degree dependent on supplies from nearby worlds -- either through plunder, taxation or trade. Reports from the Waymar Islands point towards regular shipments of minerals and victuals, as well as slaves, going off-world, most likely to the moon.
Available information also suggests a high level of fortification. Given what is known about the OUT defensive doctrine, as well as the fact that Nattland has been successfully breached once before (ref.: Morfeus and the incident concerning the Key of Ahuramazta), one can assume a high concentration of artillery, over-lapping and semi-independent defensive sections, as well as occult/arcane countermeasures.
Lastly, according to certain ancient scrolls, when the Dead Star entered the Plane of Argos, a piece broke off. This piece crashed into the far side of the moon and buried itself below its surface (note that conflicting interpretations exist). Again referring to the Legend of Morfeus, it is assumed that the Thulists were in the process of attempting to somehow harness this power when the Rogue Navigator intercepted the Key of Ahuramazta, and subsequently freed some entity from a black crystal. Which, if any, significance this has on an assault on the moon is unknown.
[Picture source 1 & 3 unknown; 2 Iron Sky]