The main airport in Belgium is the Brussels Airport, which is connected to all the major cities in Europe. The airport is not located in the main city and is situated in Flanders but there are frequent trains connecting the airport to the main city. It is the base of Brussels Airlines. Other major operators are BRU, JetairFly, Thomas Cook and Vueling. The Brussels South Charleroi Airport serves the low cost carriers like Wizzair and Ryanair. Antwerp Airport is a small, yet important one as it is very well linked to London City Airport. The other airports are Ostend Airport and Liege Airport.
Travelling by bus to Belgium is just as good an option as travelling by train is. There are bus networks like Eurolines that connect Brussels and Antwerp to cities like Amsterdam, Paris and London. Another popular bus service operator is Flixbus which also has a widespread service.
Getting to Belgium from neighbouring European countries is the best by train as it is comfortable as well as cheaper than airlines. There are direct trains between Brussels and Rotterdam, Luxembourg, Paris, Lyon, London, Ashford, Ebbsfleet, Frankfurt and Basel. Almost 10 Eurostar trains connect Brussels to London everyday. One can also travel on the France's Trains a grand vitesse, which is a high speed TGV train that connects Paris, Lyons or Geneva to Belgium.
All the major European highways like E17, E19, E313, E314, E411 and E40 pass through Belgium and driving here is a really good option. Also, the cheapest way to get to Belgium from any part of Europe can be using taxis or carpool services.
There is a ferry from Zeebrugge to Hull in England, but it is an expensive affair. There are no major waterways connection apart from this.