Princes' Street is a terrible place to walk imho. On one side of the street, a pavement saturated with hoards of shoppers, not much different than Dublin's Henry Street; on the other, nice views of the Castle, IF you manage to ignore the incessant traffic and smoke-belching buses.
Much better walking options:
Along the Water of Leith
The New Town
The Royal Mile down all the way to Holyrood
Calton Hill
The Salisbury Crags
The Meadows and Marchmont.
Cockburn Street
Princes Street Gardens
Charlotte Square, George Street and Andrews Square.