Buckingham Palace
As the current residence of Queen Elizabeth II, Buckingham Palace is a historic and intricately designed building dating back to the reign of James I in the 16th Century. While some of the Royal Family still resides in the building, they are located mainly on the north side, leaving other areas open for the public to enjoy. These locations include the Palace’s gardens and exhibitions on at the time. You can view the exterior of the palace free of charge, but inside tours are available at a price.
This is also the location of the famous Changing of the Guards Ceremony, where guards march from the Wellington Barracks to Buckingham Palace on alternating days of the week. Guards wear the iconic red coat uniform in the summer months while swapping it for a grey one in the winter. The ceremony is free for the public and lasts about 45 minutes beginning at 10:15, but be sure to save a good view point early as crowds tend to gather long before the start. The detailed schedule could be found here.