We did a walking tour of the City of London about 10 years ago and I am trying to recommend something similar to friends going for the first time. This tour concentrated on the centuries of London before all the modern buildings and recent history. There were stops/talks about the plague, the tower of London, etc. Could anyone recommend something like this that I could tell my friends about?
Could it have been with London Walks? https://www.walks.com
If it is not a regular offering they can probably do it as a private option.
For a different look at the City, Eating Europe offers a food tour. I took the tour in late June to explore the history and local food. https://www.eatingeurope.com/london/only-city-of-london-food-tour/
This guy David Harry specialises in the City of London and its history. He can design a walking tour for you or do one of his standard ones. He’s really good and also has an excellent TikTok account where he looks at quirky London history and buildings. https://thelondonspy.com/
I prefer to go at my own pace, which is extreme dawdling and following bunny trails allowed, but I will also follow published walks. I think I found a good walk in Rick Steve's London Guidebook. My copy was ripped apart and is no longer with me but I recommend your friends get a copy. He also has audioguide walks and I know I used his for a Historic City of London walk. Pretty sure the details were also in his London Guidebook.
https://www.ricksteves.com/watch-read-listen/audio/audio-tours/london
The City of London itself sponsors daily guided walks on various themes. I've seen a lot of the places they mention, and have read up on the history, but seeing it all as a unified theme looks really interesting. I'll try to fit some in during my Sept/Oct visit this year. I can always backtrack to dawdle and walk down random alleys.
https://www.thecityofldn.com/directory/city-of-london-daily-guided-walks/