The number of Grand Libraries is unknown, though most seem to assume that there are 13 of them. Frustratingly, there have been reports of Tethysi cities moving between them through some unknown means, making keeping track of them difficult. Most outsiders only enter the outer spiral, however, which is mostly kept free of water in order to welcome non-aquatic visitors. These areas are considered neutral ground by most of the civilised nations, a place of learning for all - enforced by the Tethysi, through force if necessary.
Within the control centre of each Grand Library is a vast map, displaying the entire known multiverse, with panels that can be folded infinitely to 'zoom' in or out. Countless other civilisations have sent spies to study it, who are shocked to discover it is not a secret they guard closely, for no other civilisation has managed to decipher it. By ceremonially placing a ritual pin, the Grand Library is transported to that region of space. Smaller maps located in alcoves throughout the library can be used by the Tethysi to teleport, though their primary mode of transportation is by shuttle. Most civilisations welcome the arrival of the Tethysi, but warily. Though they bring a great opportunity for knowledge, there is no guarantee that is all they will bring.
In terms of defences, though they are not primarily military structures, the Grand Libraries are quite formidable. The energy fields generated by the spiral are the rival of the most fortified planetary capitals, capable of destroying projectiles and refracting all but the most powerful of laser weapons. Should anything break through, scattered throughout the waters are prism shields and null orbs, capable of further splitting lasers or negating momentum respectively. If necessary, the entire structure can be phased half-out of reality, all attacks passing harmlessly through it, though it can still be boarded. Lining the outer spiral are colossal Erasure Cannons, a devastating weapon there is no doubt, but the primary defences of the Grand Libraries are and always will be the warriors who call them home.
The most common fuel source in Tethys 13 is Convenium, which can be sieved from its waters in its crude form. Though it can be used crude, it is far more effective when refined. It powers their shuttles, and the underwater furnaces of their forges.