Harold Lilja's laboratory

Harold Lillja's laboratory is the facility that Lillja used frequently during his dealings with the Turtles. It was located in an old industrial building that Lillja had redesigned according to his needs, such as installing a cooling unit for his computer servers.

This laboratory was where Lillja could frequently be found, and was where he developed many of his technological achievements, including  Metalhead  and  Angel Bridge's  exo-suit. He kept it under constant security surveillance. Donatello first visited the laboratory during the City Fall arc, when he was asking Lillja for equipment to help rescue Leonardo from the Foot Clan.

Upon his return from Northampton, Donatello again visited the lab, where Lillja had been developing the Metalhead robot in order to keep his lab safe from any enemies he had, such as Baxter Stockman. The robot malfunctioned, and the lab suffered severe damage as a result.

The lab became a vitally important location when Donatello enlisted Harold to build a functioning teleporter, in the hopes of defeating Krang. This led to the groundbreaking machine being located in Harold's lab, where it was used both by the Turtles and the Foot Clan to access Burnow Island. It was also the location where Donatello was mortally wounded by Bebop and Rocksteady, and where Fugitoid barely managed to save his life after transferring his consciousness into Metalhead.

The lab was also the place from which Lillja was later abducted by the Street Phantoms. After this, he was not seen in the lab by the Turtles, as he had decided to cut all ties with them and reunite with his ex-wife Libby Meitner. However, the abandoned lab was revisited by the Turtles during the Metalhead 2.0 arc, in which Metal-Don went to the lab while confused and wracked with emotional pain. They learned that he had used his weapons to blast the lab and its contents, before discovering a hitherto-secret room where Harold had left a larger, more powerful Metalhead chassis.