One of the Mega Dungeons of Lost In Space 1965 Episode #5 "There Were Giants In the Earth"

Introduction 

So I'm kicking back looking through Hulu this evening and decided to rewatch an old episode of the cult classic 'Lost In Space'. The episode was 'There Were Giants In The Earth". The basic plot goes something like this according to Wiki : 
'The Robinsons begin to make themselves at home on the strange alien world, growing plants and herding local animals for food. After checking a meteorological station, the Professor learns that a severe cold front is coming which will drop temperature to lethal levels. To make matters worse, the Professor and Major West are attacked by a giant cyclops creature that lurks in the area. The family decides to abandon the Jupiter 2 and head south to a warmer climate, but Dr. Smith refuses to go with them. Journeying in the chariot, the family seeks shelter from a freak lightning storm inside a cave. There they find ruins of a past civilization in which to explore.'

There were quite few interesting similarities between this episode and one of the original Star Trek Episodes.
 More on that in a minute. We get to see an over arching idea here of the family's fight for survival. This episode was really a glimpse into how 'Lost In Space' mankind against the universe on a thrilling small scale was supposed to work. 

Behind The Ruins On The Planet 
 
Throughout the episode there are hints that behind lurking just over the horizan is a history behind this plane the family finds itself on.  The place has the feel of some lone deserted outpost of a long forgotten alien race. 

Everything about the planet screams terraformed planet. The fact that it just happens to be  a compatible atmosphere and conditions with the human  family strikes me as vary odd. Its place screams backwater ancient colony world.
The whole planet has the feel reminiscent of the 'Isle of The Bronze' from the film 'Jason And Argonauts. This is a planet that was never meant for humans to step foot on. The race that was here before humanity was very advanced and very dangerous. Some might even say Lovecraftian in some of its aspects. 

Madness rides the star-wind... claws and teeth sharpened on centuries of corpses... dripping death astride a bacchanale of bats from nigh-black ruins of buried temples of Belial..."The Hound" Written September 1922, published February 1924 in Weird Tales, 3, No. 2, 50–52, 78
The planet that the family finds itself is not only Earth like but riddled with caverns, tunnels, ruins, and perhaps even working pits of machinery. The place has the feel of some outpost left on autopilot whose owners never returned. The gods left the place in the middle of the universe and all their toys are still in storage waiting. It might be waiting for a group of adventurers to stumble upon them. Who knows what secrets this place might hold? 

The Unclean Guardians 

'Theosophists have guessed at the awesome grandeur of the cosmic cycle wherein our world and human race form transient incidents. They have hinted at strange survivals in terms which would freeze the blood if not masked by a bland optimism. But it is not from them that there came the single glimpse of forbidden eons which chills me when I think of it and maddens me when I dream of it. That glimpse, like all dread glimpses of truth, flashed out from an accidental piecing together of separated things — in this case an old newspaper item and the notes of a dead professor...'
HP Lovecraft. .
There are races of giants that guard the artifacts and outposts of these forgotten vistas of a bygone age.These monsters almost seem to stride from legend and myth. They watch over the ruins of their former masters and reign destruction down on anyone who would dare approach. These unclean beasts aren't the only such beings other worlds also have their own primitive and unclean watchmen.
The planet is very similar to Taurus II (Murasaki 312) where the crew of the Star Ship Enterprise's Shuttle crashes in 2812. Both planets have similar characteristics. Such as: :

' Long-range scans revealed basic characteristics of this planet, such as it had an oxygen-nitrogen atmosphere.'

Other similarities among the life forms  also included : 
The inhabitants of Taurus II were order 480-G anthropoids, similar to lifeforms discovered on Hansen's Planet but much larger, ten to twelve feet in height. They were at approximately a stone-age level of technology, slightly less advanced than a "Folsom culture"

Could there be miles of tunnels and artifacts on both of these planets that have never been found because of the dangerous tribes of degenerate life forms that inhabit the planets? Generations of giants that destroy any whom they encounter because they have been genetically modified for strength, speed, deadliness and will never evolve into anything greater? Could these degenerate things be all that is left within our universe of the once mighty 'Gugs' that rule the Dreamland's underworld? Are there rites still being performed under the dead stars that are pale reflections of those that caused the gods to banish the 'gugs' to that cold nameless hell? Only the DM can decide that.

Many of the OD&D games or retroclones already contain stats for just these  sorts of giants and so it becomes a matter of simply plugging and playing the type of giant you want or need into your game. Vary the culture to keep things interesting. 

Are these giants still acting out forbidden rites to Lovecraftian gods whom they will never see again. Beings left behind to guard treasures and forbidden secrets across the stars that shall never see the light of day? 
Judge for yourselves and take a look at this cult classic right over here on Hulu
HERE