The most visible and well-known landmark in Solstice is the Great Gnomon Spire, a massive tower standing exactly one league high (15,840 feet), with a base half a mile in diameter and a spire that is (reportedly) a quarter-mile across. The Spire, as it is commonly referred to, is the anchor for the most powerful Skyward in Solstice which prevents any creature from flying more than 60 feet from a surface anywhere in the city. Roughly halfway up the Spire the strength of this ward increases to limit flight to 30 feet from a surface, and for the upper 2-3,000 feet flight is impossible. As a result reaching the top of the Spire is only possible by fighting through the traps, guardians, wards, and denizens of its hundreds of levels and is very rarely achieved.

The God-Mage built the Spire are part of his overall Necropolis, and it acts as the shadow-casting menhir of the city’s original function as a planardial. Like a sundial it shows the position of various sources of power and energy. Unlike a sundial, rather than cast a single shadow, the Spire casts eight – one a typical shadow cast by the sun, and seven others of various colors (crimson, bronze, gold, viridescent, azure, amethyst, true black, and the glowing white anti-shadow). Each of these progresses based on the relative position and strength of inner and outer planes, shooting out at different speeds, lengths, and darknesses. When one or more of these “shadows” lines up, it indicates a Planar Conjunction.

In addition to the Great Gnomon Spire’s obvious power as a tool of planar observation, the God-Mage had designed it to perform thousands of other arcane functions, and filled the interior with vast and complex mystechnological relics, summoning chambers, soul forges, rune repositories (which are believed to be the true origin of the sentient living runes, the Esigil), teleport circles, gates, portals, and communing halls. All of these he guarded with his famed Spellborn living magics, devilbound traps and objects, and the dreaded ethereals (filchers, slayers, and trapmasters), hundreds of which are believed to survive to this day (though mostly lairing in the upper levels).

To add to those risks, since the God-Mage no longer maintains his planar rituals and machines, many of his connections have broken inward, allowing quasielementals, astral roamers, and things of pure chaotic evil from the farthest reaches of the Abyss to invade inward into the Spire. Some arrive entirely by accident, while others are agents of powerful otherworldly master who seek to take control of the Spire for their own purposes.

The lowest fifty levels of the Spire have long since been cleared out and secured by agents friendly to Solstice and mortals, with the bottom two dozen housing numerous consulates, churches, guilds, and their related shops and barracks. The 36 levels above that are claimed and held by a few divine Avatars, several mortal archmages, champions, high priests, and heirophants, a pride of sphinxes, a choir of angels, a well-monitored house of devils, and a lich known as The Librarian that fully admits that it is a force for eternal evil, but also points out its not in its best interest to oppose to powerful defenders of Solstice, or risk the destruction of the plane of existence it happens to dwell on.

It is forbidden for anyone to attempt to move above these 50 levels… without a sponsor. Every guild, avatar, and denizen that the two Astrologer Guilds of Solstice acknowledge as owning a place in the Lower Fifty can sponsor an expedition by an individual or group to venture higher into the Great Gnomon Spire. The purpose of such expeditions is supposed to be to keep the various forces running amuck in the upper levels from ever taking control of too much of the structure, and to continue to explore the mysteries still undelved from the God-Mage’s time. Because of the work of the ethereals, the original machines of the spire, and the forces of Abyssal chaos, upper levels of the Spire are always in flux, making any trip up a risk, with the highest levels those that are the least well-scouted as well as the most changing and most dangerous.

Since sponsors are held responsible if an expedition causes trouble or damage that spills into the Lower Fifty or Solstice itself, most sponsors only allow experienced groups passage up, and only to deal with specific threats they believe to have arisen, through divination, rumor, or gut instinct. However some patrolling must be attempted, and as the fortunes of the denizens of the Lower Fifty wax and wane, sometimes a powerful group buy or bully sponsorship in order to undertake an expedition for their own goals… and such groups sometimes cause problems that force other groups to sponsor additional expeditions to fix what has been broken, unleashed, or awoken.

As the base of the Great Gnomon Spire abuts the Grand Arena, and is close to many of the known Dark Vaults and Warcogs beneath the city, it is assumed that connections exist between these four common adventuring areas, though if they do they are either well-guarded secrets, or temporary affairs that exist only during the proper conjunctions.