Leuven is definitely a very nice and cute Flemish city, so it makes it a perfect 1/2 or even full day trip from Brussels. Here some of the 3 most interesting streets of the city (in my opinion of course :))
The Mechelsestraat is traditionally one of the most important traffic and trade avenues of the city. Together with the Diestse, Tiense, Naamse and Brusselsestraat, it forms the network of five main axes that have shaped the Leuven street pattern since the Middle Ages. Leading from the Grote Markt to the Keizersberg - and later connected to the stone road that was built in 1730 to Mechelen - this very long and densely built street was once characterized by a narrow and winding route from its start, crossed by the Dijle river and its ramifications and up through the Voer river. The various street sections carried distinctive names up to the 19th century. (Source)
Today Mechelsestraat is known for the nice restaurants and shops that you can find along the first part of it (coming from the center) and then it goes all the way up till you end up at the Keizersberg Abby.
This 19th-century Benedictine abbey was built by monks from Maredsous Abbey. A long wall encloses the building and surrounding grounds so that the complex is reminiscent of an old fortress. The garden is a public park, offering a beautiful view of the city.
This is certainly my favorite part of Leuven in terms of looks. The houses are cute and decorated with flowers and nice elements to ensure a very cozy feeling. It's also not very known as it is not on any of the touristy roads :)
You can best enter the area (as it is not just a street) from Maria Theresiastraat. Where you are welcomed by one of Bisser's Murals. (a local streetartist from Leuven) .
Walking towards the parking area you can find some of Bisser's recent (sept. 2018) work in the city
The Street was "created on private initiative, namely by the coachman Alexander Peeters who opened and parceled out his terrain in 1835-1838. [...]This neighborhood - later also called "Mussenbuurt" - was built up relatively quickly after construction and formed a typical popular neighborhood. (Source)
If you love food, then I know that your favorite street will be this one. Packed with restaurants on both its sides, this is the place to be when it comes to get inspired on what to eat. As I don't aim to influence you on what to try, make sure you pass by this street several times ;). You can also keep an eye on BudgetGourmad's posts on IG as there are several pictures shared from the restaurants on this street
The most important event related to this street (and today all over the center) is called Hapje Tapje, when all restaurants serve tapas size dishes on stands in front of their restaurants. You can check some photos over the IG account of Budget Gourmand from the 2018 edition. this event is always on the first Sunday of August.