Nick traveled to the underground city.
The first thing he did was to delete the memories of the Ice Maiden and Piercing Heaven Base from everyone's mind, including Samar.
Then, he disconnected Piercing Heaven Base from the city.
After disconnecting it, Nick built a Zephyx generator and shoved the underground city far deeper underground.
It needed to be as hidden as possible.
Then, Nick moved Piercing Heaven Base further to the surface and moved it far away from the underground city.
It had to be relatively easy to find.
If it returned to its old position so far underground, Nick wouldn't be able to find an explanation for how he found it.
When he finished moving the base, Nick entered and deleted all evidence of human presence.
He also replaced the Zephyx generator with a different one that had a lower output.
