These three-hour, historian-led (at a PhD level) tours and thematic walks are perfect for intellectually curious travelers. Topics have broad range and are based in art history, religion, politics and urban planning. While Context operates in many cities in the U.S. and Europe, here in Boston patrons can explore the North End, chronicle the local works of artist John Singer Sargent, examine African-American history and more. Group size maxes out at 6 people. Tickets: $85. Schedule varies, check online for specifics.