The Corona Tower wall rises from ground level only when an "event" is happening on the mall. 

While promoted to the general public, the mall events are always sold out when the public tries to purchase admission. As a security measure (and to allow the human hybrids outside of the basement research complex while the events are in play), a wall rises out of the sidewalks surrounding the 64-square-block mall before each event and remains raised until the event has wound down and all hybrids have returned to the basement complex. 

The wall rises twelve feet high and seems impenetrable, although the goings-on inside can be viewed from many places in Bay City. That's the point in the lightshow that makes it appear the Tower shatters into silicon glitter and crumbles to the ground. It's all distraction, sleight of hand, a way to keep the show on the ground less obvious than the one overhead.

Getting past the wall is one of Garik Shayk's greatest frustrations. Once inside the Tower, getting out is another matter altogether.

We first learn of the Tower's wall in Book 1 of The Human-Hybrid Project, Shattered by Glass.