Benin City, which served as the capital of the Benin Kingdom, starting in the 15th century, gave rise to one of the first African art forms to be accepted internationally – the Benin brasses. Today the city is the centre of Nigeria's rubber trade, and a sprawling metropolis. The National Museum has displays of beautiful brasses.
The word sprawling could have been invented to describe Ibadan. You're likely to pass through this major transport junction, but there's little to keep you here. Hotels are generally shoddy and expensive. The best bet on the higher end is Kakanfo Inn, which has a decent Indian restaurant. A cheaper option is the University of Ibadan Guest House.
About 100km north of Lagos, Abeokuta is well known as the birthplace of many famous Nigerians, notably former president Obasanjo and Fela Kuti. The founding site of Abeokuta, the famed Olumo Rock (admission N200) has a rich history and great spiritual significance. Hire a guide (dash around N500) and climb the rock.