Castle Anthrax is a fictional stone-built 8th century fortress a few days ride from Camelot visited by Sir Galahad the Chaste in the movie Monty Python and the Holy Grail.

All residents of the castle were female. The castle was unusually well furnished, containing big beds that were both warm and soft. It was also distinguished by a grail-shaped beacon that was visible to approaching travellers.

The community comprises 160 blondes and brunettes, all aged between sixteen and nineteen-and-a-half. Galahad first meets Zoot, one of the castle's commanders. Their time was, according to Zoot, generally spent bathing, dressing, undressing and making exciting underwear.

Zoot then confesses to setting alight their grail-shaped beacon, and her identical sister tells Sir Galahad that the punishment for setting alight the grail-shaped beacon was that the guilty party is to be tied down on a bed and spanked. The rest of the girls offer to be punished by Galahad, to be followed by oral sex.

Sir Galahad is invited to inflict the appropriate penalties, but Sir Lancelot & co burst in to "rescue" him, professing the terrible peril he was in. Galahad dutifully volunteers to stay at the castle, explaining "Look, it's my duty as a knight to sample as much peril as I can" and as he is dragged out of the castle exclaims "Look, I can tackle this lot single-handed!" "Honestly, I can cope. I can handle this lot easily."