Best destination close to Belgium for weekend with friends?

Maastricht is one of my favorite Dutch cites - it's beautiful, has amazing food, and a very active night life, great bars, dancing, etc and tons of young people as there is a university there. Stay near the Vrijthof, the large square circled by great restaurants like In Den Ouden Vogelstruys. Walk from here all over the city and across the bridge. It's only 15 minutes or so to the Belgian border near Tongeren.

Maastricht has great shopping. Start in the Markt and walk down Muntstraat to Wolfstraat. There are tons of shops along this route in all price ranges - but great fashion -- Esprit, Mexx, Oililiy, Sissy Boy, H&M, and tons of shoe stores. For something to drink, try Maison Blanche Dael house roasted coffee.  If you're in the mood for a beer, go to De Bóbbel. They're both on Wolfstraat.

Keep walking and you'll run into a little square surrounded by more cafes and restaurants. Turn left and you'll run into the river, go straight and you'll run into the cool old Roman walls and canal.

The city is incredibly friendly, walkable, interesting, and fun. The food is amazing, the history and architecture is beautiful, and there's a large university there, so there's a vibrant young crowd and tons of bars, clubs, and a very active night life.

For a quick coffee and chocolate walk, check out this post: http://10000windows.com/maastricht-coffee-ice-cream-and-chocolate-the-tastebuds-stroll-of-choice/

Breda is only 20 mins away from Antwerp and has a nice nightlife, bars a located around the Grote Markt.

Maastricht every time - easy communications links, good restaurants , vineyards (no, really!) great chocolate, good hotels, and, if you really want to go mad, its in the "hilly" bit of the netherlands so if you've got a car you can have a wander around the place!

Luxembourg is a great destination - lots of great nightlife at the weekends in the Grund and uptown! 

You should go to Amsterdam. You can speak Dutch, if you're from Vlanders. Besides it's a relaxed and good city to party. Especially if you like house or techno music. 

Not far from you is Eindhoven, which is well known for it's nightlife for a younger crowd. Nearby are also 's-Hertogenbosch and Tilburg which both also offer plenty of going out options.  Maastricht is a great old town with a vibrant nightlife if you can head over that direction.

I've stayed in Brussels many times and frequently take the train to either Paris Amsterdam and London. All are great options and offer different experiences so it really depends on what you want to do. Make sure to book your train tickets in advance to get a nice discount. Happy travels!!!

A quick Eurostar trip into London could be nice -- they definitely like to go out at night! 

Paris and Amsterdam are also pretty close and good options!