Just re-watched the 1986 movie From Beyond and noticed that the female doctor, Katherine, was actually more of a main character than I’d remembered, and from her perspective, this is a Girls Underground story (not surprising, it being common in the horror genre).
Katherine meets Crawford Tillinghast once he has already gone half-mad from experimenting with a device which stimulates the pineal gland and somehow lets the person perceive creatures in an alternate (and terrifying) dimension. The doctor he was assisting appears to have been murdered, and Katherine accompanies him back to the house where it all happened, with a police officer as backup. Therefore Crawford becomes her initiator into the otherworld, as well as her companion. This is also one of those GU stories which takes place primarily all in one house. (May be worth noting, too, that Katherine is trying to find a cure for schizophrenia, which afflicted her father, so in a way there’s a theme of trying to rescue a family member.)
They turn on the machine again, and Katherine finds out that it is all real, and meets Dr. Pretorius, supposedly dead but actually assimilated to some horrifying creature on the other side – he is the adversary. After a lot of disturbing things happen (including “forgetting herself” and changing into leather S&M gear), she briefly returns “home” in the middle of the adventure, back to the regular world, but must return again to the house. Eventually, she defeats the adversary with a bomb – however, instead of a victorious ending, Katherine is driven insane by her experiences, which seems a more realistic end for some Girls Underground.