Disney's theme parks operate for 365 days a year, and often open late into the evening. That leaves little "downtime" during which they can be scrubbed and refurbished - and yet they manage to look sparkling clean every single morning. How exactly does Disney achieve this? The simple answer is through sheer weight of manpower. Every night, hundreds of Cast Members descend upon each park, each with a specific range of tasks to complete under the glow of portable floodlights. At Disneyland, for example, there are 1,500 workers in the "third shift", and many of them have worked to a nocturnal schedule for years. There is alwayssomething happening at the parks, which truly are "cities that never sleep". Here are 10 essential tasks that are completed every single night at Walt Disney World, the Disneyland Resort, the Disneyland Resort Paris, the Tokyo Disney Resort and Hong Kong Disneyland.

10. The security sweep

First things first, Disney has to make sure that its theme parks are empty before it begins any maintenance work. It's not unknown for guests to try and "camp out" in the parks at night, particularly in seemingly hard-to-spot locations such as Tom Sawyer Island. Park security, though, are aware of the most common hiding places. "If someone tried to hide, they would not stay hidden for long," Disneyland spokeswoman Suzi Brown told the LA Timesin 2010.

9. Refuelling

Many of Disney's attractions still run on good old-fashioned gasoline. Every night, a team of oiler-truckers sweeps into refuel them. At Disneyland, for example, the Columbia Sailing Ship, the Mark Twain Riverboat, the Tom Sawyer Island Rafts, the Jungle Cruise boats, the Main Street Vehicles and the Casey Jr. Circus Train all need topping up. In addition, some 104 cars on Autopia need to be refueled.

8. Safety inspections

Like all theme park operators, Disney is under an obligation to ensure that its rides run smoothly and safely. An army of engineers inspects its roller coasters and other rides, walking along tracks to check for defects, inspecting vehicles and performing other essential tasks. Firefighters also work at the parks, and carry out inspections of fire extinguishers, alarm systems and sprinkler systems.

7. Repairs

It's not just the rides that occasionally need repairing. At the Disneyland Resort, there are Cast Members whose sole responsibility is checking and replacing 800 umbrellas, 25,000 chairs and 7,000 tables in the various restaurants and snack bars in its two theme parks.

6. Production of commercials

Disney wants commercials for its theme parks to look good - and that means controlling exactly who appears in them, both in the foreground and the background. It also wants guests to be able to move freely around the park by day, without having to stop at "roadblocks" set up by production crews. For that reason, most filming takes place at night.