Maybe a bit of a spoiler.
First phase was nice but the more you read the longer those two stucks in the mansion and completing each floor, the more of her forgotten memories came back, just being stuck there was already bad and the more they learn about the truth made them both go insane in the later chapters. If horror is what you like then this might be enjoyable for you.

I dropped this manhwa long ago and dont know if i should read it and give it a chance again