Sacrifice Body ~Kodai Meikyuu ni Fuujirareta Kindan no Nikutai Kaizou Hijutsu~ by MorningStar - Adult Sex Game

It was known as The Grave, an ancient labyrinth in which a
forbidden art was sealed. Seeking treasure and fame many adventurers entered, never to return.
What happened to them?

Long thought defeated, a trio of heroines have been collected by a mysterious figure called the Grave Keeper in a stony prison deep inside labyrinth:
Sharqua the female Knight of Prauha Kingdom, Birgitta the Believer of Sophia, and Catelina "Catcha" the Summoner...