Kendo Rattan. It is a vault that inevitably draws the prisoner back to the center no matter how far the prisoner strays from it. The Void is "an endless stasis," and the prisoner's sanity would "unravel across the eons" (5:402) at the same looping millisecond. No human would ever have the capability to break free from it. Lorenzo Debray wears a pendant that stores the entire Void in it.
In Book 5: Time Jumpers, Cole learns that the Void will not hold Ramarro for long. Ramarro, being a torivor, was able to break free.