User summary:
The Secret River was the first adventure in a planned series of eight linked adventures (only the first two actually were released). The adventure was announced for the BBC Micro, Spectrum 48K, Electron, and Commodore 64 - though only the BBC Micro version actually was released.
The compact cassette included, on side A, a character generator that allowed for the creation of a D&D-like character, complete with equipment and spells.
Side B then presented the adventure. After completing the adventure, the character could be re-loaded into the generator to gain experience, rest, and recuperate - and also be saved for the next adventure in the series.
In The Secret River adventure, the character explores a cave complex and discovers the eponymous secret (and magical) river that boosts the character's capabilities.