From chapter 9, "The Virtual Reality Homebrewer's Handbook"...

"Bullfrog's 'Magic Carpet' game uses an interesting engine which seems to
use a combination of height-mapping and polygon rendering. The engine was
written in C by Glenn Corpes (Bullfrog's head of R&D), with a few hundred
lines of assembly language providing extra optimisation. A nice touch is
the "fog" which gives the game a mysterious feel, as well as restricting
the viewing distance to maintain rendering speed."

Press F1 in the game for help.