Brussels National Airport (Zaventem) 
It is located just north of Waterloo; about 20 minutes drive from the city centre. Take the Ring Road towards Charleroi / Mons / Namur.
There is also 1 train ( see section Trains )
Brussels Airport Website: www.brusselsairport.be
Infrastructure, flight schedules, access map and map of the airport.
 
Brussels South Airport (Charleroi)
It is located south of Waterloo, approximately 45 minutes drive from the city centre. Take the A54 motorway, towards Nivelles/Charleroi.
Shuttle bus (2 per hour) to Charleroi South station. From there you can get to Waterloo by bus (see section Bus "365"), or by train ( see section Train ).

Website :  www.charleroi-airport.com
Infrastructure, flight schedules, access map and map of the airport.