Darbhanga Fort, also called Raj Quila, was built in the 1930s by the Maharajas of Darbhanga, among the richest landholders in British India. Its tall red-brick walls and gateway were modelled on the Red Fort in Delhi and on Fatehpur Sikri. Work stopped after independence, so the fort was never completed. The town's palaces now house two universities.

The Navlakha Palace at Rajnagar, near Madhubani, was built in the late 19th and early 20th centuries by Maharaja Rameshwar Singh of Darbhanga. The great earthquake of 1934 left it in ruins. Its broken halls, gateways with elephant sculptures, and temples to Durga and Kali, still in worship, stand around ponds in a haunting, little-visited complex.

Lauriya Nandangarh in West Champaran has one of the finest Ashokan pillars, a single polished sandstone shaft over 12 metres high crowned by a lion and inscribed with the emperor's edicts. About two kilometres away is the Nandangarh stupa, a huge brick mound with a star-shaped, many-angled base, thought to have held relics of the Buddha.