My flight from Rwanda to Russia through Brussels. I will have 4 hours transit in Brussels airport. Can I enjoy my connection time outside of the airport till time approaches?
The practicalities of traveling to the city centre are covered in Are 7 hours enough time to leave the Brussels airport and go to the city center?
The only problem left (or not, considering that 3 hours is really short) is whether it's allowed at all. This will depend on your citizenship. If you are a citizen of either Rwanda or Russia, you won't be allowed to leave the transit area of the airport without a visa. A full list of countries whose citizens can do it is available on Wikipedia.