Cidada Velha is a city on the island of Santiago. The oldest European city in the tropics. This is an easy half-day trip from Praia although there probably won't be enough of interest to keep you there longer.
From Praia, aluguers leave from the Sucupira Market west of Plateau. Cost is 200$. Ask to be dropped at (the side road to) Forteleza Real de São Filipe. A taxi from Praia shouldn't be more than 1000$.
Aluguers returning to Praia leave every few minutes from the main square where the pelourinho is.
Even without a specific attraction in mind, there is plenty to see just walking around the historic city center, which constitutes a UNESCO World Heritage site.
Start at the Fort above the town. Tickets cost 500$ and include a map and pamphlet guide for the town.
From the fort, follow the path downhill past the ruined cathedral to arrive at the seashore. You can duck down to the beach before continuing on to the main square. The monument here is the Pelourinho ou picota and was a place of execution. Further along the Rua Banana leads up hill. This is Africa's oldest European-built street and leads to the chapel Igreja Nossa Senhora do Rośario.
Eat and Drink
There are some bars and restaurants around the main square.
Accommodation is available - ask at the tourist office.