The Museum of London ★★☆
The history of London Town from prehistoric times to the 21C, told in artifacts, scale models, archaeological finds, photographs, and paintings
The collections range from artifacts to scale models, archaeological finds to photographs, paintings to past fashions.
Best of all, it's all free.
One of the most famous exhibits is the gilded Lord Mayor's State Coach, created in 1757 for incoming Lord Mayor Sir Charles Asgill by Sir Robert Taylor for the princely sum of £860 (a cool £12 million in today's pounds).
Every time I come here, I learn something new and intertesting about ol' London town. Well worth the trip out to Barbican.
Also, though it's what looks like a dully modern bit of London—all skyscrapers and grim cement—there are suprising bits of the city's Roman-era and medieval walls poking out right by the museum and here and there about the neighborhood.
Come for the half-hour you'd expect it to take; stay for the hour or more you end up spending here.