Park your bike
There are bike sheds or stands all over the city: in shopping streets, outside public buildings and at both stations. You can leave your bike there free of charge and then pick it up later.
There are bike sheds with surveillance at Mechelen station. Report to the Fietspunt, at the front of the station between the station buffet and the bike shed under surveillance.
There are also 10 safe bike lockers at the car parks at the edge of the city at Rode Kruisplein and Douaneplein. Go to 't Atelier if you want to rent one.