My father is visiting Poland during summer. He wanted to visit Brest one day without sleepover, just in and out the same day (it's a border city, he told me). He has contacted the Belarus embassy but they haven't replied yet. Our local city council has assured him he needs only his passport to visit Brest but I fear they might be mistaken with the new rules for entry via Minsk.
Some googling has made me rather certain it is impossible to visit Brest while staying in Poland.
My parents are traveling on their own in a sort of road trip. He has no travel agent.