Citadel was a 1985 release for the BBC Micro by Superior Software. It was written by Michael Jakobsen.
It is a platform game with locked doors, keys to open them, and lots of monsters and traps to kill the player. Fairly standard platform fodder, but with some energy.
Citadel is what you might call “old school”. The graphics are very chunky and the gameplay is extremely archaic by today’s standards. Beeb fans will no doubt still love it. Everyone else will think “WTF?!” 🙂
More: Citadel on Wikipedia