Leuven lies on the edge of Flanders and Wallonia and thus at the language border. In it's early history, the river Dijle used to be the border between the teritory of the Nerviers and the Eburons. At the time of the Roman Empire, the road from Aaken to Beauvais crossed the Dijle river here.
Christianization started in the 8th century, and some of the Roman churches near the city are still reminders of that period.
Leuven was first mentioned in a text dated from 884 when the Vikings (Norman) came to settle here and got chased away by Arnulf of Carinthie in 891. In that text they called it Luvanium and Loven.
The very first dukes of Leuven are from Northern French origin, Sint Quentin.
The tourist information office is housed at the same location as the guided tour, and the inclusive book (available in different languages), costed only 25 Euro, which I thought was a really fair price. Depending on the language skill of the guide, they did translations (i.e. English, French, etc.)
Quick Tips:
Don't forget the university city (you need to make an appointment first), the Beguinage (big and small one) the different colleges, and the church where Father Damian is buried.
Best Way To Get Around:
There are parking lots for busses in the centre, but best is to look up those locations on a detailed city map.
In this city you need to walk!