S4-"Didn't We Meet At A Murder?" (Sherlock Holmes Story Plot Element)

I watched a couple S4 episodes I hadn't seen in a while, first "Goodnight Baby, Time To Die" which frankly is not a good episode for repeat viewing once you know the "twist", because on second view you get more self-conscious about how the show is a classic example of a budget-saving "bottle episode" for the end of a season (limited set, limited cast, stage dialogue).

"Didn't We Meet At a Murder?" has flaws too but it's at least more fun to watch. I noticed how the photo they used of Joanna Barnes is more than a decade old (probably from the time of "Spartacus") and how the awkward ending of her character's arrest done only with voiceovers and long-shots was clearly done because she wasn't available for shooting those sequences (that may have also been a budget issue where having the top billed guest for one less day of shooting saved more money).

What I found interesting though was that the scheme of a tunnel from one building to a nearby bank is actually a direct steal from a famous Sherlock Holmes story "The Redheaded League". And Jerome Coopersmith was certainly familiar with the Holmes stories since he wrote the script for the 1965 Holmes musical "Baker Street" that starred Fritz Weaver.

Speaking of tunneling between two buildings, how may times was it used in Five-O?

Not only in the aforementioned episode but it's also seen in S10E04 "The Friends Of Joy Kalima". We could also count S11E14 "The Meighan Conspiracy" even though that was far more convoluted than necessary. Then there's S12E12 "School For Assassins" with the trap door leading to a tunnel.

Can we think of any other instances? :)