Let me first establish that I never referred to them during gameplay as towers. This is a creative choice of Winds or the character Kallach to show us a similar image with a more familiar name. What I called them, however, is Obelisks. The name "Obelisks" is not so common and as such might not immediately bring any form of imagery to most who would read it. At least not without pulling out Merriam/Webster.
The Obelisks are Ra's Rays from ancient Egyptian times. The most famous of them in the western world would be The Washington Monument. The Obelisks look exactly like this, except at half the scale. When dormant the have a subtle inner light which glows pure white. When active, they glow violently dark red and are wrapped in eldritch energy.
The guardian is the defender and key of the Obelisks. Each one having a different guardian, I will go into detail about them when I cover specific Obelisks. In general, however, they open the Obelisks by placing a piece of themselves within it (hand/claw/etc) and pulling down, as if on a lever. The Obelisk then splits straight down the middle and parts upon itself creating two parallel half obelisks. This reveals a stairwell where the Obelisk once sit.
Entryway - After going down the stairwell the players are met with a giant double door with no obvious means to open it. Perpendicular walls to the left and right show normal size singular doors.
Going through the door on the left reveals the largest mound of treasure the characters have ever seen. Imagine Mt. Everest made of gold and platinum coins with assorted rare gem stones mixed within. Now imagine many them.
Going through the door on the right reveals a small table with a wooden bowl set upon it with a sign next to it that says simply "Tithe".
This is an obvious test. The solution of which is simply to place one tenth of your wealth in the bowl. All players must remit. If they were to try and take from the wealth in the other room, they would find that by no means can the gold leave the room. Physically trying to take the gold through the door is met with an invisible force at the doorway. All teleportation and interdimensional means of transport fail automatically, and bags of holding cannot leave the room if holding gold from it.
(This is something that Kallach's team never discovered.They always just Tithed.)
Chamber - Through the double doors the players find a large round room. The style is Roman with 12 massive pillars set in a circle around the room holding up the ceiling. On the opposite side of the room from the door is 13 Obelisks. One directly opposite and 6 to either side. Concentric circular steps rise in the center of the room. Standing on top of the steps is a man in modern day formal attire; hands held behind his back and nose pointed slightly upward.
Jeeves - He is the caretaker, in many ways, of the Obelisk. He knows of everything that goes on within it, and has certain powers over it. However, he is not real. He is not physical, even ghost touch weapons don't harm him. He is an illusion that the players can interact with to gain information about the Obelisk, although, the magic of the Obelisk prevents him from revealing certain details. He also provides a meal to the players if they stay in the Obelisk long enough. However, he never leaves that step.
Main Room- When all the players are on the top step and have told Jeeves they are ready to continue, the step lowers into the ground revealing it to be an elevator leading deeper into the Obelisk. When the elevator stops the players see a large rectangular room. A long table set in the center with nothing on it. Large double doors on the far end similar to the ones they passed through to enter the Obelisk, and a variable number of doors set in the left and right walls (dependent upon the number of trials for the Obelisk.)
This room serves as an intermission between trials. The door they pass through is standard and wooden, when they first go through, but turns green if they pass or red if they fail. Pass or fail, they cannot reenter the room. The table in the center will have food if they stay long enough in the obelisk. Eating it fully heals the players. Once the players have passed a majority of the trials, the double doors open.
The trails are where I let my imagination as a DM go wild. They can be anything. At first I intended each one to be a morality test. Then, I tried to incorporate intellectual puzzles. Finally, I said "heck with it" and used it as an excuse to try anything I wanted.
Activation Room - In this room resides the final test. This again varies depending on the Obelisk. The one thing in common between them is the sword and the stone. The sword acts as the key to activate the Obelisk. By taking up the sword and calling out a deities name you claim the Obelisk for that deity. More on this later.
A long time ago, when arcane magic was not regulated by gods, a group of wizards, exploring different dimensions, decided to create something "daring". Wanting to understand their gods better, they created a powerful magical artifact that would forcefully bring a piece of the gods home domain to the material plane. The ego of the wizards made them think, "Why should we travel there, when we can bring them here?" Thus, the Obelisks were created.
This artifact would literally bring two points on two planes together as one. Turning the interior of the Obelisk and part of the surrounding area into the home plane of the chosen god.
Knowing how dangerous such an artifact could become in the wrong hands, they placed several protective measures. They made the Obelisks invisible and incorporeal to all but those who know where (and how) to look for them. They placed a guardian with each, and made them the keys to open the Obelisks. They placed trials to determine the worth of any who enter it.
Even with the massive egos, typical of wizards, they knew they would not always be around to control the Obelisks. Not wanting their hard work to waste away with time they placed means for future generations to find and use them.
They created a compass that points to the nearest Obelisk, and shows their exact locations when placed upon a map. They created a caretaker, that will maintain the Obelisk and sustain the magic which powers it. Finally, they made all that resides within the Obelisk adaptable to the passing of time. The appearance of the caretaker, the language he speaks, and even the nature of the trials change to match the norm of the now. So that future generations won't walk in and become immediately confused by what they see and hear.
Time passes on, and the magic of the Obelisks wanes. The invisibility and incorporeality spells on the Obelisks fail entirely. Revealing them to the world. Inside, the stability of the magic that governs the trials becomes unstable. Now the trials may no longer test participants in the way originally intended.
This covers, I believe, the Obelisks in full detail. If you have any questions let me know. If enough interest is expressed in continuing this series; Next is "The Island".