For his third and final adventure, museum security guard Larry (Ben Stiller) travels across the Atlantic with his teenage son (Skyler Gisondo) to London's British Museum. There, he seeks to repair the malfunctioning stone tablet that's been bringing exhibits such as Teddy Roosevelt (Robin Williams) and cowboy Jedediah (Owen Wilson) to life. This time, the action spills into the streets. The gang rides a double-decker bus, says director Shawn Levy, while Sir Lancelot (Downton Abbey's Dan Stevens) can be seen ''on a real horse galloping through Trafalgar Square.'' We suspect Guinevere prefers the Tube.