The Technodrome on Balaraphon.
Balaraphon is a planet that was inhabited by a peaceful species native to Dimension X seen in the 1987 TV series. They were attacked unprovoked by an invasion fleet led by Krang and Shredder, but saved thanks to the interference of the TMNT, who had arrived on the planet. The Turtles' arrival on Balaraphon was the final phase of a plan by Shredder to exhaust and trap them after a period of exploration in Dimension X. It is also the scene of the Technodrome's final destruction, as it was dragged down into the pit of a tentacled creature after its engines were blown out by the TMNT whilst escaping Shredder's trap. (Turtle Trek)
Balaraphon is seen again when Donatello and Michelangelo travel there to retrieve Krang's Android body from the ruins of the Technodrome, which now sits atop a small hill. (Divide and Conquer)