In the past, admins who wanted to build a spawn would sometimes store their work in the adminworld, likely for safekeeping or in case they were still working on it. Sadly, most of schematics that were on the server in the past are mostly lost (including many spawns).
However, some of these spawns survived. Unbeknownst to the builders and admins at the time, these spawns would end up becoming relics of their time, several years later.