A cross between a cable car and one of the sleek light rail vehicles that run underground along Market Street, San Francisco’s fleet of historic streetcars runs aboveground on Market Street between the Castro District and Fisherman's Wharf. And to learn the full story behind these historic cars, visit the free San Francisco Railway Museum. There are great photo ops, simple didactics that explain the history of the fleet and a gift shop with unique items and memorabilia. The whole experience is right on track for little train buffs.