Pokoge ~Shokujara no Tou~

Jet-black towers in the secluded mountains are rumored to bear countless treasures. Many adventurers ventured there, but none have returned. Today a new group of female adventurers come to the tower. They are captured and forced to play a game with the lord of the tower and his tentacle minions. If they win, they gain freedom. But if they lose, there is no limit to the humiliation to suffer.

[From vndbreview]