Leuven is mainly about the main square and the bars - not so much more to see other than for a few shops and canal. It's a very beautiful place with many restaurants and a few small weekend markets.
Perfect town: big enough to have everything you need, but small enough to know every corner, do everything by foot and not have any of the issues of bigger cities.
One of the oldest and the best Catholic university in the world is here. If you like rainy misty and cool weather, it is ideal for you. Also, irish pubs are famous.