When the Vault Dweller enters the map, all that can be seen (beyond the usual desert dust) is a large blue police call box. These were a common sight on the island of Great Britain during the 1960s. When the Vault Dweller approaches this strangely-located object, the light on top starts spinning, and the box slowly vanishes into thin air with a whooshing sound, leaving behind only a motion sensor.
Behind the scenes
This encounter is a reference to the British sci-fi show Doctor Who, and the blue box is the Doctor's time travel machine, the TARDIS (Time And Relative Dimension In Space), which is bigger on the inside.