I was surprised to bump into quite a few tourists in Lima who couldn't be bothered to go to the historic part of the city - they thought it would be boring and/or unsafe and preferred to stay around the beaches and the touristy areas. I think they missed out!
There are some really beautiful buildings here and you can easily spend a day checking them out and having a relaxed meal or drink in one of the squares.
My two highlights - and must sees for everyone - are the Monastery of San Francisco and the main cathedral. They are absolutely stunning inside. Don't miss the tomb for Pizarro in the cathedral.