In an org that named their servers after planets, we turned off "Mars" (which was actually completely and utterly undocumented) and discovered it was the bridge between the intranet and the internet. However, upon turning it back on... Nothing came up again.

There were no logs to try and work out which processes needed to launch for it to do its job, causing several days of website downtime (not a simple website - dozens of interconnected services). We ended up taking the phone off the hook because we kept getting calls of "is it fixed yet?"