There are footpaths all over Penwith, so it's a great destination for walking.
The most spectacular walks are often the coastal ones, with truly breathtaking views. The coastal path is generally well signposted, and well maintained, but can be quite rugged, as it undulates up and down the granite cliffs, and generally distances feel further than they appear!
The moorland walks also offer some lovely views, especially when the gorse and heather are in flower. A large number of Penwith's ancient sites can be found up on the moors, the footpaths tend to change a bit, but popular destinations are well signposted.
Bear in mind that the weather can be changeable, and not everywhere gets a mobile phone signal! Take all-weather gear, a map and water.