Any places nearby Patna for weekend getaway?

I am currently put up in Patna and visited most of Bihar famous places like Rajgir, BodhGaya. Any other places where I can visit in and around Bihar, I am planning a road trip. I have already covered Nepal, Siliguri, Gangtok, Varanasi, Ranchi , any place else you can think of? How is Darbhanga fort? Any place else?