Travel to Brussels
The closest airport is Brussels Airport, also called Brussel Nationaal/Bruxelles-National
It has a good train connection to the main Brussels stations.
Somewhat further away is Brussels South Charleroi Airport, also called Charleroi Airport.
It is used by low-cost airlines. You need to take the bus or bus/train to get from there to Brussels.
High-speed trains connect Brussels to various European cities. Check here for details
For more detailed information consult the website of the Observatory.