Viator connect me with Subculture Tours in London. First rate all the way. I booked a private tour, as I had only a three hour window to see all the highlights. My guide, James, has a Masters in History, and swung me by eight palaces, the changing of the guard from the guard headquarters front row, the royal gardens, in the tube, through the alleyways, all the while thorougly entertaining me with dates and historical facts. This was my first visit to London, I had only four days and many business obligations. HIGHLY recommend!