Immeasurably old and enormous, the Cascade undoubtedly has many secrets left for its current inhabitants to discover. However, quite a lot is known already.
The discoverers of the Cascade's hubworld, and creators of the fractal structure, intended for it to be impervious to attack, and they seemed to do fairly well.
Swarming around the hubworld are quintillions of tiny trans-temporal entities constructed of stringshard, that will rapidly pin down and then wipe whatever they hit from the timeline. Reaching the Cascade from extrauniversal space is therefore somewhat akin to maneuvering through a fierce storm of ultra-deadly needles.
All portals opening into the hubworld from the Wall are carefully monitored by advanced computer systems, such as Vyotekha, which will dispense huge numbers of tactical drones and weapons up to galaxy-smashing yields if anything hostile comes through. Any collateral damage is usually cleaned up by careful timeline manipulation.
In addition to the huge number of deities and hyper-powerful leaders who rule sections of the Cascade, there are six individuals, whose identities are kept secret and blended into society, called the Hexagon Lords. They possess unimaginable power beyond all but the most powerful eldritch abominations or God, and are devoted to stopping threats too powerful for the other defenses.
Millions of supercluster-sized plates of stringshard, taking hexagonal and pentagonal shapes, serve as base plates for cities the size of entire galaxies to be built. These cities are meticulously organized, though no two are exactly alike because they are all built by different civilizations or species altogether.
When cities do not suffice for holding exceedingly large beings, colossal cubical living spaces are built on the underside of each base plate, with gravity manipulated so that the buildings and such are not damaged.
The primary power supply for the Cascade is a series of gigantic metamesonium reactors collectively outputting as much power as is desired; this can be scaled up to infinite quantities if necessary thanks to metamesonium's properties, though normally the output is capped at 10200 watts for "reasonable" purposes. (This puts the civilizations managing the Cascade at upwards of Kardashev Type 19, according to Sagan's system for calculating the types.)
It has a number of auxiliary generators that operate by forcefully creating crossover events between nearby megaverses, and then harvesting the huge amount of energy released. Such an event is only performed when the metamesonium reactors fail and the Cascade simply needs power for a short time (to help open up portals and evacuate its residents, for example).