Parque de la Muralla (Park of the Wall) is located behind the San Francisco Church directly at the banks of the River Rimac. In this park remains of the old city wall that once protected Lima from invading pirates and the rising waters of the Rio Rimac were unearthed. Today you can see around 300 meters of the nicely restored city wall. The small on-site museum displays pieces and artifacts found during the excavation and explains the history of the wall.
The park has a miniature train for the kids, nice walkways and benches to sit down and relax. It is more designed for families, but even if you are on your own it's worth a visit. Actually it's a surprisingly quiet and restful place amidst the crowded, hectic Historical City Center. Don't miss the restaurants, souvenir shops and of course the statue of Francisco Pizarro, the founder of Lima.