Goree Island was as far as I travelled this week. It is about a 15 minute ride on a ferry boat.
The last time I was in Dakar, I travelled to Kedougou, a town in the southeastern region of the country, to see the Dindifelo Waterfalls. It took over 25 hours to get there by road.
I took several taxis and one car rapide. Car Rapides are colorful buses that you will often see photos of in association with Dakar. They act kind of like public buses but are privately owned and don't have reliable routes or pickup times. You simply ask the driver where he's going, and if it's in the direction you want, you pay 100 CFA (15 cents) and hop on.
When I visited Goree Island, I stayed with a family that lived on top of the tallest hill on the island. The owner, Rasma Makha, has planted 1,000 plants since moving there!