The icy caverns were constructed inside a warehouse previously used for cold storage, and required truckloads of lumber and 10,000 square feet of Styrofoam. The set was one of the most expensive and elaborate built during the series' history, requiring a constant temperature of negative 21 degrees F (negative 29 degrees C) to maintain the real snow and ice used to decorate it. This refrigeration allowed the actors' breath to visibly fog up, aiding the cast in having a place that felt real for their acting.
The first season finale not to feature The Cigarette Smoking Man.
This marks the first time we see one of Scully's adult brothers, played by Pat Skipper. The actor had filmed a scene for Memento Mori (1997) but it was cut.
The first cut of the episode was 12 minutes too long so Chris Carter re-edited it two days before transmission.
First appearance in the series of Charles Cioffi playing Section Chief Blevins since Conduit (1993).