I remember this story from about twenty years back hitting the news:
https://www.theregister.com/2001/04/12/missing_novell_server_discovered_after/
Missing Novell server discovered after four years
In the kind of tale any aspiring BOFH would be able to dine out on for months, the University of North Carolina has finally located one of its most reliable servers - which nobody had seen for FOUR years.
One of the university's Novell servers had been doing the business for years and nobody stopped to wonder where it was - until some bright spark realised an audit of the campus network was well overdue.
According to a report by Techweb it was only then that those campus techies realised they couldn't find the server. Attempts to follow network cabling to find the missing box led to the discovery that maintenance workers had sealed the server behind a wall.