It is not at all hard to get on a train and travel from Brussels to Amsterdam. In kilometres it is much closer than for example London, but the trip lasts one hour more due to the slower train. But, the advantage with Amsterdam is that the city is much easier to digest and it can almost be done with in one day. Amsterdam has a special atmosphere and the most important things to see in Amsterdam are not attractions, but museums. The most famous museums in Amsterdam is probably the Van Gogh Museum and the Anne Frank house, both worth a visit. Since the city does not boast in attractions, this is a city ideal for a day trip, and for those who would like to see and visit one more European capital during their visit to Brussels.
If you want to travel with train to Amsterdam, you can find more information at Thalys. For more information about Amsterdam, visit the Amsterdam Guide. If you would like to join in on an organised trip to Amsterdam, visit Viator.