Bizerte is located in the north of Tunisia, approx. 65 km north of Tunis. It is the largest city north of the capital. Bizerte is not on the tourist track so you may actually have a chance to see some real Tunisia here. The main reasons to come are the unspoiled traditional quarter of the old port, and a couple of good beaches in the area.
The main draw in the medina is the enormous Kasbah. With its massive walls it looks out over the northern side of the entrance to the old harbour. Originally a Byzantine fort built in the 6th century AD, the present fort was built by the Ottomans in the 17th century. There is also a smaller fort called Ksiba, which actually also means small fort, which houses a small but interesting oceanographic museum.
Around Place Bouchoucha in the heart of the Ottoman town you find the lively fish market, the Great Mosque and the Youssef Dey fountain. Up on a hill overlooking the town there is the so-called Spanish Fort. As far as I know it's actually Turkish.
Outside the old town, La Corniche and Sidi Salem Beach are where Bizerte's summer life happens. Further afield, Cap Blanc — the northernmost point of mainland Africa — and the migratory bird sanctuary at Lake Ichkeul make good half-day trips.