Situated roughly in the center of Sigil's Guildhall Ward, the Great Gymnasium did, and still does, function primarily as what its name implies. The calm beauty of the Great Gymnasium in many ways rivals or exceeds the laurels given to the glory of other buildings of the ward, and indeed the city. The gymnasium’s entire outer façade, and much of the inner structure, is built of a unique and evocative black marble laced throughout with veins of gold and rose colored minerals. While before the Faction War the Great Gymnasium was also the home of the Transcendent Order, it was and still is a place where most any basher can go to improve their body by a great variety of physical activities.
The structure is composed of a grand front portico that rises up to front the central tower of the gymnasium. The first level extends to both sides of the tower and back, while the second floor comprises the tower and a top layer to the front of the left and right wings. The third and least frequented floor is that which comprises the top of the tower.
Dominating one of the exterior walls of the Great Gymnasium is a gigantic painted mural, gifted without any request for it nearly six years prior by a member of the Xaositects. Called simply the Painter, the tiefling up and decided to paint the wall one day, following her winds of whimsy. In the end, she created one of the most moving and beautiful paintings in all of Sigil. Abstract in nature, and as varied as the whims of the Painter herself, two different bloods can look at it and claim to see a different pattern within its chaotic - or perhaps simply complex - depths. Regardless of what one claims to see within it, it is evocative to most all that look upon it, and the Ciphers were not in the least ungracious to the Xaositect who took it upon herself to gift it to them for naught.
The first floor is dominated by the exercise field used for various martial arts and combat skills. The center of the field also sports three pools, one hot, one warm, and one cold. Beyond the field is an inner portico used for musical and other public artistic demonstrations and lectures. Past the portico are a number of separated rooms for music, dancing, sculpting, and other artistic endeavors as well as sealed and warded rooms for spellslingers to practice their arts without harming themselves or others in the process. Those who frequented the old building still come for much the same, and aside from some of the faction high-ups wandering and giving token words to those training or practicing (especially Rhys, who rarely says a word, but then usually something profound), the former members of the Transcendent Order hold no more sway over the place than any others.
The second level was previously filled with a number of meditation chambers, including one taking up most of the floor called the Shared Meditation Chamber, and a few additional training rooms for use of faction members only. Now open to the public, old members and new bashers seeking some calm from the bustle of Sigil and their own lives frequent the chambers for quiet contemplation.
The Cadence of the Planes Chamber, a mysterious room once open only to highly placed Ciphers, is located at the apex of the Gymnasium’s tower and now sits open to the public. Be that as it may, few besides those Ciphers and those seeking them for training in the philosophy of the Transcendent Order frequently arrive to utilize the room. It’s not advertised in the least by the new operators of the Gymnasium, seemingly out of respect for the former owners, as a rush of berks seeking it out for their own ignorant curiosity would defeat the purpose of the chamber. The chamber itself functions as a total sensory deprivation chamber. Inside, the light is extinguished, temperature is held constant and cool, and slight, regulated air movements within keep the atmosphere pleasant and calm. The Ciphers used some manner of magic to produce a constant levitation field within, allowing a single user of the chamber to sit floating and undisturbed from everything but their own heartbeat and thoughts. Or isolated from thoughts, as the Ciphers might say. Indeed some non-Ciphers who have entered the chamber claim that not only does the Cadence Chamber seal off the user from sight and sounds outside the room, but also isolates them from stray thoughts detectable by psionic individuals. Others say they have sensed a dulling of magic within the chamber. Not quite an actual antimagic field, but something removing the influence of any spells outside the chamber from being expressed within.The Ciphers themselves claim to be able to use the Cadence of the Planes Chamber to remove the sounds, influence, and distractions of the multiverse to let them listen to the Cadence of the Planes. By listening to the heartbeat of the Cadence in time with their own inner rhythm, they can act in harmony with the multiverse, knowing what to do at any given instant. The Cadence chamber still stands, and while many dismiss the metaphysical philosophy of the Ciphers, clearly there’s something to the Cadence or the chamber itself. After all, that same something apparently told former Factol Rhys to simply leave Sigil in order to avoid the the Faction War.
Sources: Text excerpted from Chapter 7 of Planewalker's 3e Planescape Campaign Setting material.
'Factols Manifesto', 'In the Cage: A Guide to Sigil'.