Hey there! I've never personally been to Gambia, but have done a little reading on it. I also found one travelog about a week's cycle trip through which I didn't get a chance to go thoroughly through, but there may be info that would be useful to you.
Gambia travelogWhat were you hoping to do during your week there? There are some very lovely sandy and picturesque beaches if you just want to relax. There are a few wildlife parks with some pretty amazing animals to be seen; Abuko Nature Reserve and Kiang West Nt'l Park as well if your into wildlife. Banjul looks like a pretty major town for the area and is said to have cool markets and really inspiring architecture. You can also go upriver from Banjul, stopping at places like Juffure (said to be the homeland of Alex Haley, writer of the
amazing book "Roots"), James Island, Tendaba and Wassau, which all seem very interesting. Well, check it out b/c it looks like a trip upriver could be very rewarding.
Hope that helps a
little bit!