The Ninja Turtles fighting Krang inside the Technodrome in the 1989 arcade game. Technodrome portal seen in background.
The Trans-Dimensional Portal in the Technodrome of the 1987 video games. Usually, Shredder and Krang appear through it.
In the U.S. manual for Teenage Mutant Ninja Turtles II: The Arcade Game, the portal is referred to as the "Translocation Matrix Beam," through which Shredder recruited two bounty hunters from across the universe: Tora and Shogun.
In Turtles in Time, it is also used as a time portal.