the radio, as seen in rp_industrial17_v1
The "Magic radio" as it is known, is a radio present in the maps rp_c8, and rp_industrial17 (and many of their variants).
The radio is known to have magical properties due to people being able to glitch through walls or invade the nexus solo.
Many fascist server admins will delete or freeze this prop to stop solo-minges from griefing into the nexus, however there are still many methods that aren't easily blockable, so removing the radio doesn't really help.