So I'm a Spider, So What?, Vol. 13 (manga) by Okina Baba
In the midst of an ancient ruin (that look more like a spaceship than a ruin) our party boldly makes their way!! But, uhh, we make have accidentally awakened a weapon from the distant past...or would it be future? I mean, it does look like a UFO...Agh, not another last boss fight!!