Lemmino creates amazing documentaries about a wide variety of topics (DB Cooper, JFK Assassination, Jack the Ripper). He uploads very infrequently, but it's totally worth it when he does.

Barely Sociable is similar in style and uploads high quality pieces about various mysterious occurrences.

Drachinifel uploads frequent, well researched content about naval history from the age of sail to the 1950s.

Our Own Devices is a very small channel that feels similar to Technology Connections (another excellent channel). He uploads content about the history and inner workings of old devices of all sorts.

Throttle House is the best car channel on YouTube.

Jason Cammisa's Revelations series on the Hagerty channel has really good deep dives into the histories of some important cars.

Aging Wheels/Under Dunn are excellent car and/or wood project channels. Chickens make frequent appearances too.

Mentour Pilot has excellent analysis of airline crashes.

Jay Foreman uploads funny and informative content about maps (Map Men) and tidbits about the history of London.

Cathode Ray Dude uploads deep dives into weird computers, computer peripherals, and old cameras. I've watched his half hour video about modems at least 5 times.

Mustard uploads excellent content about crazy ideas in transportation (like the Soviet love affair with the ekranoplan).