If real state is a premium at that location, going down might be cost effective, or maybe the only way to get it done due to a number of reasons. But I've never seen/heard of substation built with that many levels. Maybe someone here can chime in.
There has been an on going effort to harden our infrastructure for several years now. Some critical components have video surveillance.
A nearby town to our north had an old Nike Missile site. It was either before Y2K or after 9-11 that DHS/FEMA turned the abandoned site into one of their facilities. Lots of communication towers added.
Ma Bell used old nuke bunkers several stories down along the ocean for undersea cables.
https://www.chicagotribune.com/news/ct-xpm-1985-02-10-8501080634-story.html