The static shot of the capital of the Federated Peoples' Republic opening the story is actually a photo of Rouen, France. The spire near the center is Rouen Cathedral, which for four years in the 1800s was the tallest building in the world.
When Barney is using the remote control to remove the bolts from the detonator, the grip say NAF 1173-2. This is the control grip that was used in WWII US Navy and Army Air Corp fighters as the control stick.
Dr. Wimmer is treating Anton Malek for an incurable illness. The actor playing Dr. Wimmer also played Caesar Rodney in 1776 (1972), who has incurable cancer.
This episode is the first time this season that the new large corridor set, with the distinct illuminated suspended ceiling is used.