1d6 Random Dangerous Mythos Adventure Locations Table of the 'Old Solar' System

There are dangerous places that people forget about where deep under the Earth the remains of the past are coming to impinge on the lives of those above. Cycles of Earth live, breath, and die but are seldom gone. With violence & weirdness these place burst upon the Earth. They're legacies in darkness & horror awaken when foolish adventurers and trespassers stumble upon them.

Thasaidon, lord of seven hells
Wherein the single Serpent dwells,
With volumes drawn from pit to pit
Through fire and darkness infinite —
Thasaidon, sun of nether skies,
Thine ancient evil never dies,
For aye thy somber fulgors flame
On sunken worlds that have no name,
Man's heart enthrones thee, still supreme,
Though the false sorcerers blaspheme.
— The Song of Xeethra

The Dark Eidolon  (1935)  by Clark Ashton Smith

In the shadows of former glory & power mankind has built & rebuilt his destiny. There are places that seldom get mentioned today for they have grown wary & tired in the ways of the world but below the surface an evil and depravity sleeps to awaken every eon or so. Places whose names are lost to history but whose legacies live on amid the realm of legend and forbidden mythologies.

Wise is the adventurer who consults a scribe or sorcerers of the forbidden or the black arts upon the history of these places if he or she can even find such an individual. These scribes are often jealously guarded or secreted away by black magick guilds or the like. The cost of such a consultation will be at least 100,000 gold pieces and or a minor artifact of magic or super science. There are demonic powers from Saturn & the outer worlds that can be consulted but they are best left alone. Adventurers however are not wise nor the most patient of individuals.
"I have helped you heretofore in all things," said the image, with stony and sonorous accents that were echoed metallically in the seven silver lamps. "Yea, the undying worms of fire and darkness have come forth like an army at your summons, and the wings of nether genii have risen to occlude the sun when you called them. But, verily, I will not aid you in this vengeance you have planned: for the emperor Zotulla has done me no wrong and has served me well though unwittingly; and the people of Xylac, by reason of their turpitudes, are not the least of my terrestial worshippers. Therefore, Namirrha, it were well for you to live in peace with Zotulla, and well to forget this olden wrong that was done to the beggar-boy Narthos. For the ways of destiny are strange, and the workings of its laws sometimes hidden; and truly, if the hooves of Zotulla's palfrey had not spurned you and trodden you under, your life had been otherwise, and the name and renown of Namirrha had still slept in oblivion as a dream undreamed. Yea, you would tarry still as a beggar in Ummaos, content with a beggar's guerdon, and would never have fared forth to become the pupil of the wise and learned Ouphaloc; and I, Thasaidon, would have lost the lordliest of all necromancers who have accepted my service and my bond. Think well, Namirrha, and ponder these matters: for both of us, it would seem, are indebted to Zotulla in all gratitude for the trampling he gave you."
The Dark Eidolon  (1935)  by Clark Ashton Smith

1d6 Random Dangerous Mythos Adventure Locations Table of the 'Old Solar' System 

1. The Fragment of Naree'a - This place is slightly out of phase with the local time space continuum as it orbits in the shadow of Jupiter. There are hundreds of Yithians dealing with and engineering time/space engines of incredible cosmic design. Anyone landing on or even encountering them will be captured and taken to the great vaults below the Naree'a structure for preservation. Here there are seven floors of ancient and forbidden treasures a waiting the alien agenda of the Great Race. 
2. The Singing  Deserts of Titan - The moon titan once contained and will again the great deserts made from the nanite sands of a long forgotten race. They are or were the alien memories of their long forgotten creators but on days when the sun shines upon this world. The starlight sparks memories and long forgotten cities rear themselves into existence for 1d10 months. Those who land here might become a part of the memories as the nanites tear them apart and make them a part of the permanent collection. However anyone who is able to collect a vial of this sand may be able with super science computers or magick might reconstruct the lost database of racial memories of this long forgotten race.  
3. Cript Castle - This ancient ruined castle of human design is long since gone but seven levels below it there is the house of light an ancient Elder Thing processing and research complex within it are the biological echoes of a long gone segment of the Elder Thing's history. Those venturing into this complex will be assaulted by the telepathic memories of the Elder Things. The victim genetic structure will be  changed by the viruses and bacteria that live on the walls of this place feeding on the incredible power that still courses through the place. There are thousands of gold pieces worth of Elder Thing equipment & relics but its guarded by the undead mutant things that venture down here. There are rumors that they are evolving. 
4. The Play Pen of The Genii - This was once a strange energy cube that belonged to an ancient strain of the Mi Go. The place now rests below a monastery's ruins. For thousands of years the order that worked here summoned demonic essences from beyond for their own benign purposes. That time is now long gone and there are strange genii energies that wish to break through and ravage the land. There are several thousand gold pieces of magick equipment and treasure here left by long forgotten peoples or things. 
5. The Crypts of Rru - There is an asteroid that houses 1d8 ancient vampire lords who guard seven cryptic books of the ancient god Thasaidon. For thousands of years their dreaming song of praise has kept the demonic god in check but now adventurers might disturb their sleep of the ages. There are several thousand gold pieces in funeral treasures here. For now they sleep, dream, and wait. 
6. The alien sorcerer of Vru waits and watches above the roaring winds of Jupiter held in place by ancient time/space generator. His thoughts and dreams take the shape of alien monsters and demons long forgotten. He watches the alien god thing that Jupiter holds prisoner and has for millions of years but he needs adventurers for a suicide mission. He can offer a thousand relics or secrets but he must act soon for his master
   Thasaidon, lord of seven hells is impatient at best.