Nightdive Studios' quality remaster of Star Wars: Dark Forces is an excellent way to revisit Kyle Katarn's first adventure, a landmark FPS that would give rise to some of the best lightsaber action games ever. As pointed out by the Twitter account of Dark Forces/Jedi Knight fan site df-21.net, the remaster also preserves a bit of FPS history with its restoration of cut level, the ISD Avenger.
The Avenger served as a demo level at the Consumer Electronics Show prior to Dark Forces' original release in 1995. It seems to have been an alternate first mission, with Kyle Katarn storming the titular Star Destroyer and making off with the Death Star plans in a commandeered TIE Fighter—just the vanilla kind, not one of its cooler (or lamer) variants.
The story goes that it was replaced with Dark Forces' first mission, Secret Base, after LucasArts determined it was too difficult an introduction for new players. Crucially, one final clue to its existence made its way to retail: a screenshot of The Avenger's wireframe map was left on the big box release, tantalizing players with a mission they could never access in the game proper. You can check out the evidence yourself on a 3D scan of the packaging thanks to the online Big Box Collection—it's on the spine with four screenshots, second from the LucasArts logo.
DF-21 credits open source Force Engine creator luciusDXL with helping Nightdive recover the mission—it was apparently present in the original LucasArts development vault Nightdive used in remastering the game, but had to be converted to a new file type and stitched back together into a playable form.
The result can be played directly from Dark Forces Remastered's main menu, separate from the rest of the campaign. I can understand LucasArts' concern for new players—the final process for accessing the Death Star plans is more than a little obtuse, requiring you to flick a switch revealing a secret room, flick another switch that opens up a hatch in the secret room, then find a concealed entrance to the ship's air ducts off to the side in the bridge.
The thing is, that's Jedi Knight and Dark Forces to me! Until 2003's Jedi Academy, the final game in the series by Raven Software (now of CoD: Warzone fame), "not knowing where the hell you're supposed to go" was one of the essential, defining traits of Kyle Katarn's adventures.
I still fondly recall getting lost in the final level of Jedi Outcast on a recent replay, looking up a guide, and finding the video's creator stuck and running in circles in the exact same place I was. This was baked into the series from the very beginning, its first public playable form, and now it's preserved for posterity thanks to this remaster.