Mont des Arts
One of the best places to visit in Brussels for free is Mont des Arts, which translates to "Mountain of Arts". This is an area in central Brussels and was built under the orders of Leopold II. This king clearly had a lot of influence over the city and created lots of monuments that remain in modern Brussels.
In Mont des Arts, you can find landscaped gardens, statues, fountains, and other displays of public art, stairs leading up to a spectacular view, lots of museums, the Royal Library of Belgium, and the National Archives of Belgium. Many of the other Brussels attractions are located within walking distance of this central hub, so you'll definitely pass through here a few times while exploring Brussels. Mont des Arts are great for photo opportunities and for acting as a starting point for sightseeing in Brussels.
Location: City of Brussels, Brussels-Capital Region