Theen is located on the shores of an inlet of the Cerenarian Sea, between the kingdom of Ooth-Nargai and the hellish lands to the northeast. Theen is built in a style of architecture very strongly recalling that of the ancient Greeks. The entire structure is built of a bizarre sort of metallic stone. This metallic stone helps to give Theen its serene and peaceful appearance and the stone's luster at various times of the day has given Theen another name, "Dark Sun."

Sometime in the past (Dreamlands time being notoriously difficult to estimate, but sometime since the quest of Randolph Carter) an attack was launched on Ooth-Nargai by Zejul-far-Hith, a hardy war-leader from the wastes north of Lhosk. The Zejul's people were among the only human followers of the long forgotten god Mordiggian. The nomads unleashed the Breath of Karakal on the peaceful monks of Theen, a seaside monastery, and surrounding regions in northern Ooth-Nargai. Finally, with the aid of the patron god Nath-Horthath, the Zejul's forces were decimated, the few survivors fleeing back into the Forbidden Lands.

The survivors of the plague that the Zejul had unleashed were gathered into the monastery. In a lengthy ritual, the high priest of Theen invoked the power of Nath-Horthath to cure all those afflicted. Unfortunately, the god Mordiggian intervened, and the victims were not cured, but merely preserved. They exist in a ghastly state of half-life, the disease having ceased to progress. However, the symptoms remained, and in addition, they were cursed with immortality. All the inhabitants wracked with terrible agony and rendered nearly mindless, it was only a matter of time until they turned to evil.

The monastery has since become a sort of self-contained, miniature theocracy. Nonatus, the high priest at the time of the plague, still rules Theen, unable to die or even be killed. Since the time of the plague, the people of the city-state have come to regard Nath-Horthath as their forsaker, ignorant of Mordiggian's role in their ultimate fate. Nonetheless, the people of Theen venerate Mordiggian (in fact, it is the last bastion of that god's worship, outside of vast sections of The Underworld), and the vengeful goddess Hagarg Ryonis.

Those unwitting few who accidently visit Theen have to cope with the attitudes of the inhabitants. The Theenites are fiercely independent, and tolerate no intrusion into the monastery. They will mercilessly pursue the outsider, eventually capturing him and feeding him to the ghouls, a number of which live in the monastery.

Theenites all display the symptoms of the Breath of Karakal, a severe form of fever which caused the afflicted to feel unbearably hot and, eventually, to be incinerated from within. As a result, many inhabitants of Theen go about completely nude in an effort to escape the unbearable heat. All inhabitants are constantly drenched with perspiration, often to such an extent that they appear to have been dunked in the sea.

In the case of an outsider who contracts the Breath of Karakal (65% likely upon entering Theen), the disease is almost invariably fatal within 2-3 weeks. It is rumored that the disease can be cured by the roots of the Nakor Tree, native to Oriab. As the victim of the disease incinerates from within, witnessing a death from the plague requires a SAN roll (1D4/1D8).