The Plaza de Armas in downtown Lima was planned by Pizzaro in 1535. It consists of the Presidential Palace, The Cathedral, and City Hall.
The Presidential Palace is not open to the public and security around the plaza is quite heavy. It is possible to take photos of the guards and the palace, but ask first. The Catherdal was begun in 1746 after the first one was destroyed by an earthquake. On the right hand side as you enter, you'll see the remains of Pizzaro. The carved choir stalls were a gift of Charles V to the first cathedral of Peru. The Museum of religious art inside the cathedral is also open to the public. There are many beautiful paintings from the 16th and 17th century there.
There is an admissions charge and extra charge for cameras.