It is a city with universities as well as with huge expat communities. I have never seen a city with even just one expat communities or university without nightlife.

For the days there are museums, there is the Atomium and there is a Mini Europe close to it.

You could leave the city and see something of the Flanders countryside, even the WW I battle sites and war graves.

And you can of course just go to one of the squares, find a nice place to sit and have a few beers, Belgium is famous for those, deservedly so. Try some of the local brews, talk with the waiting staff what will suit you best.

Me and my friend were planning to,do a road trip round Europe, and go to Brussels! But is there actually anything to do there? What's the night life like, and what is there to do during the day?

Drink beer. Eat mussels. Chocolate.

Buying a bus ticket to the Netherlands.