From what I'd read in 2005, after their April wedding, Prince Charles and Camilla (who took the title Duchess of Cornwall after the marriage) spent their honeymoon at Birkhall, a three story palace within Balmoral Castle, the royal family's summer residence in Scotland. Birkhall is formerly owned by the late Queen Mother, after her death it passes to Prince Charles.
After getting married, Prince Charles took Camilla to spend their honeymoon in Scotland, Bir-khall. They had spent very happy time there.