This was an very uncharacteristic outdoor stunt for Houdini to perform. At this time, the suspended straitjacket escape was his outdoor stunt of choice. But "Human Flys" were all the rage in the 1920s, and this was a time Houdini was promoting himself as a silent movie action hero. So this Douglas Fairbanksian display makes sense when viewed through that lens.
What's also intresting is the stunt didn't seem to draw a crowd. "A man was doing remarkable feats on the castle parapets yesterday afternoon, and yet not one of the hundreds of passers-by seemed to notice him," the paper recorded. But I expect this was because this wasn't an advertised stunt. It may have been an impromptu performance while visiting the castle, or a demonstration for photographers. There are several photos of Houdini on rooftops and staging movie-like action on landmarks during this time.
However, news of Houdini's stunt seems to have cast a spell over the populace of Newcastle. A few days later a large crowd gathered below St Nicholas’ Cathedral, having heard Houdini planned to climb the Cathedral's spire at 5:15pm. But Houdini was in his dressing room at the Hippodrome and unaware of the rumors. The crowd remained in place for over an hour. The next day the Chronicle reported they were "probably still there."
Read the full article, With Houdini and Doyle on TV now, we recall when Houdini came to Newcastle, at The Chronicle.