The scene of a collapsing train bridge is partly without models. The overhead shot of a train crossing a bridge was full scale, but the bridge collapse was a large-scale miniature, verifiable by observing the slightly jerky motion of the rear passenger car as the train pulls away, as well as the slowed-down water droplets which are out of scale in the splashing river below. All the steamships shown in the first half are miniatures shot in an outdoor studio tank. The exception is the American ship shown at the intermission point, which is real. A tunnel was built for a train sequence out of paper mache. After the train filming was complete, the "tunnel" was pushed over into the gorge. Many of the special effects are described and pictured in a 1956 Popular Mechanics article. The scenes of the crossing of the Atlantic Ocean by steamship took place off San Francisco and were shot on a specially built prop steamer, a converted barge mocked up to resemble a small ocean-going steamship, with mock paddles driven by the electric motor from an old streetcar. In his memoirs, Niven described the whole thing as being dangerously unstable (though stability improved as it was dismantled as though to feed it into its own furnaces as the plot required). One of the most famous sequences in the film, the flight by hydrogen balloon, is not in the original Jules Verne novel. Because the film was made in Todd AO, the sequence was expressly created to show off the locations seen on the flight, as projected on the giant curved screen used for the process. A similar balloon flight can be found in an earlier Jules Verne novel, "Five Weeks in a Balloon", in which the protagonists explore Africa from a hydrogen balloon. Many of the balloon scenes with Niven and Cantinflas were filmed using a crane. Even that height bothered Niven, who was afraid of heights. Tom Burges, who was shorter than Niven, was used as a stand-in for scenes where the balloon is seen from a distance. Many of the lots used in the film are now on the land occupied by Century City, an office complex in the L.A. area. In his memoirs, Niven related that Todd completed filming while in considerable debt. The post-production work on the film was an exercise in holding off Todd's creditors long enough to produce a saleable film, and the footage was worked upon under the supervision of Todd's creditors and returned to a secure vault each night, as if it were in escrow.