Time bridge

A time bridge was a form of time travel used by the Third Doctor. While stranded on 20th century Earth and working for UNIT, he experimented with his Time-Space Visualiser; in the presence of a spacecraft fragment saturated with omicron radiation, the Visualiser was able to create a time bridge connecting to 1934 Salutua, where the spacecraft exploded. (PROSE: The Eye of the Giant)

Omega's anti-matter organism served as a time bridge, transporting those it came into contact with into Omega's anti-matter universe. The First Doctor informed his second and third incarnations of this, asking them what a bridge was for. When the Third Doctor gave the correct answer ("crossing"), the First Doctor told them to "stop dilly-dallying and cross it!" (TV: The Three Doctors)