Holodeck

Entertainment, Training, & Investigative Descriptions
in 2261, a prototype holodeck had been developed, but malfunctioned
By 2364, the tech had improved enough to allow Starfleet to install them on ship
Enable holographic projections; through photons contained within force fields
Could generate holographic images that appeared to extend for an unlimited distance
Equipped with safety protocols to prevent serious injury, could be turned off
Required their own power source, separate from all other ship systems