The closest international airport is Brussels airport (BRU) which is located about 12 kilometers in north-eastern direction to Brussels. You can reach the city center by taxi (approximately 30 Euro) or by train (approximately 3 Euro).
You can also reach Brussels very conveniently by train. The most international station close to the city center is "Gare du Midi". You have access to all public transport systems and can reach your hotel and Université Libre de Bruxelles easily.
You can find more detailed information on the public transport system of Brussels here.
The meeting will take place at "Salle Solvay" at the 5th floor of building N&O at the Campus "Plaine" of Université Libre de Bruxelles.
To go to the university from the city center, take the metro at station "Bourse". You should get off at the metro station "Delta" (line 5, direction "Herman-Debroux"). At station "Delta", follow the signs to "ULB/VUB". There is a pedestrian path which takes about 10 minutes. You will pass along the cafeteria on your right hand side. Then continue and enter building N&O on your left. You can find a map of the campus here.