Star Trek: The Experience was an immersive themed attraction which opened in 1998 at the Las Vegas Hilton and closed in 2008. For anybody who ever experienced it, this is incredible behind the scenes footage of them building the set, including a lights-on view of the transporter room mechanism at around 11:45.
For those unfamiliar, you basically walked into a simulator loading area, and then using a bunch of lighting and mechanical trickery felt like you were being beamed onto the Enterprise. It was an incredible effect, and actually seeing how it was done has solved a mystery that has plagued me for years. I may or may not have notebooks filled with "transporter room" and question marks scribbled from cover to cover.
Keep going for the full video, as well as as a promo video showing what the original attraction was like.
And video of what the experience was like when it was in operation: