Everyone will need a visa except citizens of Switzerland and Israel.
Visas can be single entry or multiple entry, but multiple entry is recommended more than single entry. Multiple entry visas usually last a year, whereas the single entry last three months.
They cost $150 and take two days to process.
By ship
Other African cities and countries are accessible via boats and barges that travel infrequently along the Ubangui river. The Ubangui River flows into the Congo River, which is navigable all the way to Stanley Falls near Kinshasa/Brazzaville. Although slow, there are regular although adhering to no set schedule barges which travel from Bangui to Kinshasa/Brazzaville.
By bus
Bus service is available from Cameroon and Chad, although the length and the dangerous countryside makes such bus trips infrequent. In terms of safety and ease of passing through checkpoints, however, traveling by bus is preferable to traveling by 4x4.