The most densely populated area of Africa, it is many ways both the continent's most difficult place for travel and potentially its most rewarding.
The African highways connect many cities in West Africa with Nigeria being the main hub.
Flying from other African cities can be dangerous as many airlines have a very poor safety record. Check this first before choosing to fly with an airline.
In order of size here are the main airline hubs.
Generally it takes time - and a whole lot of patience - to move around in West Africa. The roads are not all in great conditions and many roads aren't paved. Always be sure to have an extra day or two in the end if you are going somewhere since planning is very hard when the transport is unreliable.
Well, there actually isn't too much to see here! Visitors who focus on sightseeing will find themselves experiencing a lot of hardship with pretty small payoffs. A common traveler complaint is of spending all the time in miserable bush taxis! The big game animals of the rest of Sub-Saharan Africa are absent; the magestic ruins of North and East Africa likewise are nowhere to be found. In general, time spent searching for "attractions" can be better spent getting to know the people you are visiting, engaging in a real and meaningful cultural exchange, starting to understand their history, religion, and way of seeing the world.
That said, though, we're all travelers here, it's hard to stay in one place, and chasing down sights is a good way to slake wanderlust.
Historical monuments dating back past the arrival of Europeans in the region are few and far between. Tropical weather took its toll upon the larger structures built by old kingdoms and empires, and those that survived the weather often were destroyed with some incredible violence by European invaders (the destruction of Benin City in Nigeria being a prominent example). The most notable structures of African past would likely be the enormous collection of ramparts, walls, and ditches at the ancient fortress of Sungbo's Eredo, less than 20 miles from Lagos, and the palaces of the Dahomey Empire in Abomey, Benin.
Many of the sites of significant historical interest in West Africa are European-built. The terrifying slave castles of the ian coast (most famously at Elmina and Cape Coast) are imposing on their own for their massive size and seaside locations, but their importance to the history of the modern world cannot be overstated, and are a must-see for anyone in the region. Sites of importance to the slave trade are hardly limited to the charismatic forts of Ghana, though, with prominent sites near Dakar, Conakry, aforementioned Abomey, Porto Novo, and Freetown (with sites especially important to the slave trade to the United States in Freetown).
Go to Benin if you´re interested in voodoo because this is where it originates. There should be plenty of opportunities to go to voodoo festivals and fetish markets.
West African food doesn't seem to be for everyone, but those who like it love it. The staple dishes are starch plus some version of soup. Rice is the most popular starch, but fufu—a thick paste, with the rough consistency of soft play-dough, usually made by boiling starchy root vegetables in water and pounding with a mortar and pestle—and other similar pastes are a more interesting alternative. Fufu and its cousins should be eaten with the right hand, and usually dipped in the sauce, stew, or soup provided. Simple "chop bars" (there are plenty of different names for this common phenomenon) nearly always provide this recipe, plus some chicken or fish.
Street food is delicious, multifarious, and dirt cheap. Unfortunately, problems with sanitation make this food a bit more dangerous than those found in chop bar-style spots and restaurants, for the straightforward reason that you aren't sure when it was cooked! Items that you see cooked, items that require peeling (e.g., eggs, coconuts, bananas, etc.), or items wrapped immediately after cooking (like bread) are safe.
Restaurants in cities are very skewed towards European dishes, and tend to treat African food like a poor man's diet. The Francophone countries often have a few excellent French restaurants hidden in the larger cities. What constitutes a "restaurant," though, is malleable. The restaurant could potentially be just a log for sitting, and be defined a "restaurant" simply by dint of having more than three dishes available.
Make sure your water bottles are sealed and not just refilled with tap water. It can be hard to see until you actually test the top, but people are generally honest about this sort of thing. Many travelers try to go for the locally produced mineral water, rather than those produced by foreign corporations, since local economies need all the help they can get.
"Pure water" is also widely available in guaranteed-sanitary sachets sold on the street, usually for less than 5¢, and is a great way to make sure you stay hydrated in the hot climate. Coconuts in most of these countries are also omnipresent, and street vendors will take off the top with a machete for a tasty drink.
Lagers, non-alcoholic malts, and some weird beverage masquerading as "Guiness" are among the more popular beverages you will run across. For harder stuff, look around for palm wine and gin sachets (which mix well with sprite, or more foolishly, palm wine).
As far as disease goes, West Africa is the most dangerous place on the planet. It is probably the one place on earth where you should go to extremes to protect yourself from mosquitoes. Do not sleep without a net and do not go without malaria medicine. If you develop symptoms, go to a clinic immediately to make sure of whether you need treatment. Malaria is about as common here as a runny nose, and the worst strain (which is by no means uncommon) can kill you in 24 hours. The parasite will likely live with you for the rest of your days as well, with high risk of recurrence. There is no vaccine.
There are plenty of other scary tropical diseases to protect yourself from in this region. The other big dangers for which there is no vaccine available, include common Dengue Fever and Schistosomiasis, various other creepy parasites, Lassa Fever, River Blindness, and the more rare Ebola virus.
Many diseases, happily, can be prevented via vaccination. Visit a travel clinic before traveling to the region to find out exactly which immunizations you will need, preferably giving yourself ample time to get the shots taken care of! You need a yellow-fever vaccination to enter most (if not all) of these countries. Rabies vaccination is generally considered optional, but it is a terrible disease to get, with 100% mortality if untreated, and you're most likely to contract it far away from decent medical services.
Are the dangers posed by road travel really greater in West Africa than the rest of the developing world? Yes, probably. Travel by boat is notoriously unsafe throughout the region as well. Traffic accidents kill more travelers than disease in West Africa. There isn't a whole lot you can do about this, unfortunately. The most important step to take is to avoid overland travel after dark. Other steps available to those traveling more luxuriously would be to get a trusted driver with a larger 4WD vehicle, and to just generally avoid the rickety minivan bush taxis driven by fatalistic maniacs. Moto-taxis are quite unsafe as well (if often by far more convenient than any other form of transportation...).
West Africa gets a worse rap than it deserves for crime. Actually, it's possible this bad reputation is just Nigeria's fault. Outside that one crime-legend, West Africa just doesn't have the sort of problems with street crime that you'll find in East African capitals, in South Africa, or for that matter the United States! Countries such as Ghana, Sierra Leone, Senegal, Burkina Faso, Cape Verde, and most of Togo and Benin are so refreshingly free of violent crime.
Traditionally a volatile region, and, alas, currently a volatile region. The culprits are easily identifiable and avoidable, fortunately: Guinea, Liberia, Côte d'Ivoire, Guinea-Bissau, and to an extent Nigeria.