Fort Jacques was erected during the burst of fort-building following independence in 1804. It was built by Alexandre Pétion and named after Jean-Jacques Dessalines, and though it is well preserved, the structure was slightly damaged in the 2010 earthquake. The ruined Fort Alexandre is a short walk away. Overlooking Port-au-Prince, they both offer breathtaking views. The forts are a 3km walk or moto ride from the main road – take the sharp uphill road opposite Fermathe’s covered market.
At the time of research, the fort was closed for renovation, which means you can't go inside (but also nobody is there to collect the normal US$3 admission). It's pleasant enough to walk around the exterior, where you get the best views anyway. It's unclear when it will reopen.