The scene with the stage car that the characters use to be lowered down to in the film was created by using a rubber rolling 8 foot wall that looked like the inside of a cave to give the illusion that they were actually going down beneath the surface.
The original draft of the script featured an alternative opening, which would have addressed the inconsistency between the different versions of the first film (the US version omits the final scene, where it's revealed that Sarah's escape from the cave was a hallucination). The opening scene would have shown Sarah following a vision of her daughter into an abyss and ending up in a lake that would take her outside the cave. This explains why the dog used to trace Sarah's steps later in the film stops at the lake, rather than the side of a mountain as per the ending of the US version of the first movie.
In the beginning most of the other original cast members besides Sarah from the first film would return, some in flashbacks, dreams and possible hallucinations. It was Neil Marshal's idea in the end to Jon Harris to go about bringing the original cast to use through Holly's camera instead.
The original cast from the first film returns to film the video camera shots featured in Part 2. Executive Producer Neil Marshal who was director of the first Descent wanted to flesh out the recording that Holly had made on her camera in the first Descent.