If you decide to cross from Kinshasa to Brazza, be aware that: 1) you'll need different currency in Brazza, which uses the CFA Franc (FCFA) valid in various West & Central African countries. Kinshasa uses Congolese francs. 2) If you're planning to come back to Kin, you should check your entry visa for DRC - if it doesn't allow multiple entries, you'll have to pay for another one to get back because even though you're only going a couple of miles, and the 2 cities are almost one, you're leaving the country. 3) It's worth paying someone (trustworthy!) to go to the river port with your passport and get your Congo-B visa in advance, as it can be a long wait for one if you try to get it when you arrive at the port.