Friskis&Svettis is a fitness and sports organisation that hosts pop-up work out classes around Brussels and the world, including free sessions throughout July and August. It entirely run by volunteers with more than 12,000 volunteers working as fitness instructors throughout Europe. There are 500 people in Brussels that are already members. One of the organisers, Alex Mascia, says it's a laid back approach to fitness.
www.friskis.be