From Brussels, if you wish to travel to other cities (within/outside Belgium), the main train station would be the Midi station which serves as the central point. There are 2 types of ticket you may consider according to your need and budget - A single/retun ticket to 1 city or a 10-single-way pass to any city. One of the benefit of the second type of the ticket is that you can share it with your friends. At the end, you might be able to save up some money.
Here is my returned ticket from Brussels to Antwerp
A guy is selling food and beverage inside the train.
Antwerp was the first city I explored in my list =) It's known as a diamond land where you can see many shops selling diamonds around however I was not going there for the sake of diamond. There are still a lot of magnificient, historial and interesting landmarks to see. Due to the time contraint, I only managed to visit 10% of the tourist spots -.-'
Upon arrival at Antwerp Central station.
The Antwerp central station itself is one of the must-visit-place.
The view from outside the station
I didn't know Belgium has this, too! It reminds me of my childhood's favourite.
Grote Markt, located at the city square
These beautiful Guild houses are found nearby the city square
The Antwerp Cathedral of our Lady. A great masterpiece!
Can I have a hotdog burger? (Sorry, we are closing!)
Or perhaps some fries over here?