The final season Robin was finally old enough to drive the Batmobile. Back in the 1960's the age to drive was 16, however the legal age to drive in Britain was 17 for a vehicle (with some smaller motorbikes placed at 16 years of age). So, Batman still wanting Robin to obey the laws while overseas, let Robin drive the Batmobiles before legal age in Britain.
When he was signed for this episode, Rudy Vallee was enjoying something of a comeback, via his successes in the stage and film versions of "How to Succeed in Business Without Really Trying." Unfortunately, he also had a reputation for being famously difficult to get along with, a reputation which he proceeded to justify during the taping of this three-episode story. Yvonne Craig described it as nothing less than "three weeks in hell." Conversely, Glynis Johns was very easy to work with, according to Adam West, and got on well with everyone in the cast and crew.
This was Madge Blake's final appearance as Aunt Harriet. She had all but retired due to illness and made only two appearances during the final season.
The title references the Tower of London where prisoners used to be kept.
Both Batman and Robin, separately, discovers Batgirl's bag near a bush, realizing that opening it would mean to discover the girl's true identity; each of the Dynamic Duo decides not to open it, in order to preserve her secrecy.