Is this for use with Greyhawk, or a Homebrewed world? If Greyhawk, then the Sea of Death is the Sea of Dust, and the Dead God is Tharizdun, worshipped by the former inhabitants thereof, mostly wiped out by the Rain of Colorless Fire (see
Sea of Death, part of the "Gord the Rogue" cycle by Gary Gygax). If not, you might use Darnizhan, from Michael Moorcock's Melnibonean mythos. Anyway...
Oswestry (which might be in Tehn, in Greyhawk) is a desert oasis on the shores of lake Perpalis, shielded from the winds of the Sea of Death's dust by the Dragonspine hills... Missing from the map is the fact that there is a great drop-off all along the Sea of Death, which is surrounded by mountains. Thus, one must go down from the plateau where Oswestry sits, through steep mountains, to come to the floor of the waterless sea far below.
The entire area of the map is basically desert. Oswestry is an oasis, and the Oghm River which feeds it flows down over the mountains near the lighthouse, where it disappears into the mountains, never getting far into the Sea of Dust.
The Stone Nomads roam the Stonelendings to the north and east of Oswestry. They are a tough, barbaric breed of giant lizard riders. They are important because they are among the few who venture into the outskirts of the Sea of Death and the lands of the Goldworms.
The only arable land in this region is around Oswestry (where some evergreens acacia/yew, and a few other plants survive in the acidic soil), and certain portions of the Oghm River Valley, where the land is sheltered from the winds, and well watered.
The Temple Complex is a temple to Tharizdun/Darnizhan. In the first case, he is "dead", but imprisoned in a fortress on one of the seven heavens. In the latter case, he is "dead", but angry about it, and is actively seeking a way to "come back". In either case, dead gods aren't permanently dead, and Tharizdun, at least, has cultists actively searching for the (Tripartite?) keys to release him - and they aren't nice people!
The Goldworms are metallivores brought from the Sea of Death long ago, by ignorant, greedy men. They burrow through the earth, eating iron, pyrites, silicates, and organics, and casting the gold often associated with them, in this region. Originally brought here to mine the region, they quickly escaped into the wild and grew out of control, ruining the soil (except along the river, where it is too wet for them). Thus, the Stone Nomads were forced out of their former territories, to the stonelands (similar to the Nevada Badlands, in the USA). In time, as the soil was depleted, only those Goldworms able to go the deepest were able to survive, the rest dying off. Thus, the 100-or-so survivors are the size of Giant Purple Worms, AC 0, and with a Hardness of 10-15 (depending upon your PC's abilities in combat and magic). A few (large) lumps of cast-off gold can be found on the surface, perhaps, but must will be deep underground, in slimy worm-tunnels. Tranport of these solid lumps should pose a problem, without a portable hole...
The Stone Nomads, here, can play the part of Dune's Freemen, and have the skills and techniques to ride them, call them, and/or scare them off, if the GM wishes.
The Lighthouse is a mystery, as the Sea of Dust was never a true sea... Obviously, it is a remnant of the civilization of former worshippers of The Dead One, but exactly what it is remains a mystery, even to the Stone Nomads brave enough to climb around it. While a light sometimes shines from it, no way in has ever been found.
[Probably, that's because the Nomads are looking in the wrong places... It could be an observatory, with a rotating head, which (now uncontrolled) rotates with the seasons, occasionally letting the light of a
Continual Flame inside shine out. The entrance would be underground, near where the "surface" of the land used to be, now under the metallic, acidic dust, not up around the top where the Nomads have been looking... Here, besides a ruined telescope and astrological equipment could be found a small complex to explore, and samples of the ancient language to decipher... Who knows? Perhaps clues to Tharizdun's first key, or notes that "the stars are right" for Darnizhan's return. If the former, it is in the Temple Complex. If the latter, then a method of stopping the return/defeating the Dead One might be found.]
The mountains around the Sea of Death are pretty barren, with occassional (rare) valleys of Stone Nomads (small permanent settlements, wherever there is water).
The Sea of Dust is a vast desert of black ash, metallic wastes of Goldworms (long extinct, here), acidic salts, poisonous plants (where there are any cacti), black puddings, rare, hostile, hungry vermin and very few animals, and the giant lizards who can live upon such fare. Near the center are outcroppings of buried buildings, which lead to the underground tunnels linking the few surviving buried cities, where the degenerate descendants of the Dead One's worshippers still lurk, below the light. The black desert, above, is frequently whipped into flesh-eating storms of the acidic, ashy, metallic sand, which will quickly kill, strip, and bury anyone caught in it, unprotected. Only the Stone Nomads know how to survive these storms, and even they don't go beyond a day's travel into those wastes...
So, whatever is at the "X" is best reached down the river, then around the encircling hills (although getting back will be tough). What could be worth risking the waterfall over the mountains, the storms of the Sea of Death, and the more general hardships of the desert? Well, you could ask the Wizard... The wonderful Wizard of Oswestry!
Maybe it's where Darnizhan sleeps. Maybe it's a treasue. Maybe it's the Elephant's Graveyard where the last, great Goldworms come to die...
