This is an amazing stop motion movie, made almost entirely by one person, Takahide Hori.
The premise is quite simple: in the far future humans live on the top level of some immense structure. They have evolved into cyborgs but can no longer reproduce. The lower levels are populated by clones which have rebelled against them. In order to recover the secret of procreation, an explorer is sent down. He is shot down by the clone air defences, but his head is recovered. Then begins a series of adventures in a world full of casual brutality, in endless corridors with xenomorph-like monsters and other strange creatures. It is amazingly done with quite a bit of gore at times. If a young Peter Jackson had run the Aardman studios, they would have produced something like this.
There is a short version on youtube, which is more or less the first part of the long movie.
https://www.youtube.com/watch?v=ge18Ieyi9bI
