This park is 2 miles south of the city center and easily accessible via the 38 bus. Bois de Cambre is a little larger and more rugged than Parc Bruxelles and Cinquantenaire. There are lots of lovely paths, including ~1 mile around the lake. At the northwestern end of the park is the University of Brussels, and at the southern end is a golf course and hippodrome. It’s about 3.3 miles around the perimeter, with lots of paths to make a longer run. Bois de Cambre is the beginning of the Sonian Forest, a 10,000+ acre forest with 5k, 10k, and 20k loops.
Alternative from downtown: Using Ave. Louise, ~2 miles