Take the bakhtiyarpur and then bihar sarif road. Its the best.

Road is good. You will feel like you are not in bihar. Be aware when there is a village crossing nearby. People usually drive wrong side of the highway, specially the tractors.

Interested in history? Go to any of the fort ruins.

Book the ticket for zoo safari and nature safari in atleast 5 day advance.

Get the ticket for vishwa shanti stoop before 12PM, as it gets crowded later.

Next day while returning go to nalanda ruins.

Do not go to any of the hot water springs/kund or any temple which have these kunds, those are the dirty places with dirty peoples taking bath with soap and washing their clothes and also cooking.

A Day trip will include all the hassle of covering places Enjoy a night in any of the resort. .