According to Disney employee guidelines, all Cast Members must wear Mickey Mouse print underwear while on the job, subject to random inspection.

The Imagineers had a difficult time rendering audioanimatronic animal forms, so they used actual taxidermy animals in many attractions.

To expand on this...

There is a tribute of red long johns to those who have died on Disneyland property. It didn't start with the death on BTMRR, but is often attributed to the red long johns that appeared in the campground shortly after the accident occurred.

Disney security has permission from the FAA and the US Military to fire warning shots at low-flying aircraft violating the air space above any Disney Park. In the case of international parks, it varies depending on local treaties.

The 2nd stories of the buildings that line Main Street are shorter than the first story. They were built to house offices for the actors that served as character models for the 7 dwarves (there were actually 20 of them on staff so the animators had a variety of character designs to choose from). They were never used for their intended purpose because they didn't pass California building safety codes.

Many of the buildings at Disneyland disguise missile silos, and the USAF maintains and staffs a control bunker under the train station.

The DLRR has access to outside rail lines and can be used as troop transport in case of a national emergency.

They'll use the tunnel that runs under the entry plaza between DCA and Disneyland...

The rotating section of Innoventions is actually capable of very high rotational speed and is used as a giant clothes dryer at night by the costume department.

If you scream loud enough on Matterhorn, avalanches will kill the people waiting in Pixie Hollow.