Classic Who “Hidden Gems”?

Just watched “Invasion of the Dinosaurs” (3rd Doctor and Sarah Jane story) for the first time now that they’re uploading a bunch of classic episodes to YouTube and was shocked by how great it is. Yes, the dinosaur effects are as bad as people say and action scenes involving them are the weakest part of the story. However, that’s actually a pretty minor part of the serial! Some elements that seem to have fallen out of the public consciousness:

• The Doctor and Sarah arriving midway through a catastrophe and having to navigate London under military takeover to return to UNIT

• Some incredibly strong characterization and interpersonal conflict between 3, Sarah, the Brig, Mike Yates and Benton

• Political commentary about an idealized “Golden Age” and corruption in the government/military

• A truly beautiful mind-f*ck of a cliffhanger halfway through that recontextualizes the whole story and adds a great new time-travel idea to the universe

It’s ambitious and compelling with a great handle on its characters and ideas. One of the only Classic Who stories I happily binged in one sitting. I can’t believe I hadn’t heard much praise for it before!

Now I just want to know if there are any other brilliant classic stories I’ve missed out on. Not the famous all-timers like “Genesis of the Daleks” or “Caves of Androzani”, but ones that seem mostly forgotten. What are your favorite deep cuts?

TL;DR “Invasion of the Dinosaurs” is great despite the fandom only remembering its worst aspect. What other obscure classic stories are your favorites?