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 nevere 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) 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.