Lima is a great city to explore -- I must state that up front -- but the central historic district which composes the World Heritage Site was not as impressive to me as other historic districts I have visited in Latin America, such as Mexico City or Quito. Walking through the district in October 2018, I made brief stops in Plaza San Martin, centered around a statue of its eponymous hero on horseback, and the Iglesia de La Merced, with its neat baroque facade, before making my way to the more charming Plaza Mayor. This plaza turned out to be the most fascinating of the historical sites I saw in the city center (to include the San Francisco Convent); perhaps it was because the sun finally came out to shine on the yellow-walled mansions with box balconies surrounding the square, or perhaps it was the unexpected military band playing in front of the palace. That said, my best memories of Lima aren't from the historic center, but rather from exploring around the coastal Miraflores and Barranco neighborhoods, walking through the Magic Fountains at night, hiking around the Pachacamac pyramids outside the city, and enjoying an excellent dinner overlooking the ruins of Huaca Pucllana. Lima as a whole is certainly worth a visit.
Logistics: Lima's historic center is very walkable; it is also accessible from many other parts of the city by bus.