In the original Devilman TV series the Himalayas are simply the resting place for the demon Tribe that are planning to prepare an attack upon humanity. Whilst on a expedition Professor Fudo and his son Akira Fudo fall down a crevice in the ice and stumble upon several demons Rerasu, Daruni, Devilman and the leader Zennon who kill the humans and after a breif battle with Rerasu and Daruni Devilman takes over the body of Akira Fudo.
In the manga the Himalayas are the place that the demons were sent to hibernate to escape death by God. Thousands of years later however they slowly thaw out and manage to escape.
Devilman: The Birth/Demon BirdEdit
In the OVAs the Himalayas are being explored by Professor Fudo, his wife and his assistant Yamanobe when they suddenly are attacked by thawing out demons, yamanobe is killed by falling ice whilst the Professor and his wife are devoured by the turtle Demon Jinmen.