Leave the greasepaint in the hotel room. These tours are for those with intellectual leanings. Context bills them not as hammy storytelling sessions but as “walking seminars,” some several hours long and for premium rates, hosted by professors, historians, and other scholars. For example, one of its 2014 additions was about London’s role in the colonial slave trade, a topic most museums ignore. Some tours are only available to groups, but inquire about availability.