Lust for Darkness Key

Jonathan Moon receives a letter from his wife, who had disappeared a year earlier. Following the information in the message, he heads to an isolated mansion where a hidden eldritch ceremony takes place. The gates open to another world - the profane and perverse realm of Lusst'ghaa.
Move both in a Victorian mansion and in Lusst'ghaa - an alien dimension full of creatures from other worlds. Lusst'ghaa was similar to our Earth until the local beings decided to suffer a total degeneration, at their own will.
Through experiments they transformed their bodies so that they never ceased to experience carnal pleasures. Hundreds of years have passed since that metamorphosis, and Lusst'ghaa is now a land invaded by extraterrestrial vegetation and full of monstrosities that contort in an endless ecstasy.