Gao is not a very attractive city. For those crossing the Sahara, it is however the last or the first place where one can get some comfort.
The town has never quite recovered from Moulay Ismail’s raid with his Moroccan warriors in 1591 despite its prime location on the Niger River.
Gao is also quite a hot place to be and self appointed guides can be rather pushy, so you may want to move on quickly. For this purpose (moving on) Gao is an excellent place. It is a link between the routes north to Tamanrasset, east to Niger, and west to Bamako.
Sights include the rather uninspiring Musee du Sahel (a museum featuring art, tools, household items) markets (leather work, desert sandals, knives and swords), the busy port and the tomb of Askia (a 500-year-old adobe pyramid with a view of the river and town). Another highlight is an early-morning pirogue ride to the big red sand dune just out of town.
Leaving Gao, one can take a pinasse on the River Niger to Timbuktu, a journey of roughly three days which most guides can organise. You will spend the three days watching the life on the riverbanks and the fishermen on the river, but should also enjoy the bird life (kingfishers, ibis, raptors), hippos, and for the lucky few a sighting of the elusive manatee.