Smith finds a cyborg-making making machine in a cave.
Not a classic but reasonably entertaining. The season three episodes before seemed to be getting away from the traditional season two "Will/Smith/Robot find something weird in a cave" theme, and here we are going back to it again. But, generally speaking, this is not done in the silly year two tone - so all is good.
The touching ending alone makes the whole hour worthwhile and it is nice to see Guy Williams (John Robinson) look so happy as he gets involved in a few fight scenes.
Voyage to the Bottom of the Sea connection: this series had an episode - The Cyborg - where the cyborgs would all dress like these guys.
Fantastic Voyage (1966) connection - that tunnel thing the cyborgs climb out of was actually apart of the human body in Fantastic Voyage.