If any one of Rajasthan's many forts were to be singled out for its glorious history and chivalric lore, it would be Chittaurgarh. It's also gargantuan in size, and there's plenty to explore on a day trip from Udaipur.
This was the capital of the Mewar princely state from the 8th to the 16th centuries, before Maharana Udai Singh moved the capital to Udaipur, and the sprawling hilltop fort occupies roughly 700 acres on a hill about 300 feet high. It was besieged and sacked three times: after the first two conquests, the Rajputs recovered it, but the third attack clinched it for the Mughals for several decades.
The first attack took place in 1303, when the Sultan of Delhi Allauddin Khilji became so enamored of Rani Padmini that he set out to attack the fort and win her in battle. Some 34,000 warriors lost their lives in this struggle, but the Sultan did not get Padmini: she and all the women in the fort committed jauhar—mass self-immolation—in anticipation of widowhood and assaults by invading armies. Frustrated, Khilji entered the city in a rage, looting and destroying much of what he saw. Chittaurgarh was also the home of the saint-poet Mirabai, a 16th-century Rajput princess and devotee of Lord Krishna who gave up her royal life to sing bhajans (hymns) in his praise.
The massive fort encompasses the palaces of the 15th-century ruler Rana Kumbha, where Udaipur's founder Udai Singh was born, as well as palace of Rani Padmini. Legend has it that Khilji fell in love with Padmini by gazing at her reflection in the pond in front of her palace. Also worth visiting in the fort are the victory towers—the ornate Vijay Stambh and Kirti Stambh —and a huge variety of temples, including Kunbha Shyam, Kalika Mata, and the Meera temple associated with the devotional poetess Mirabai. The Fateh Prakash Mahal displays some fine sculptures. Plan to spend at least half a day in Chittaurgarh. Note that the sites are spread out and it can get quite sunny, so you may want to drive between some points. You can find a guide by the Rampole entrance to the fort or near the Rana Kumbha.