Castle of Riddles is a text adventure released by Acornsoft for the BBC Micro (in 1982) and Acorn Electron (1984) home computers.
The player takes the role of a 'professional adventurer' who is 'down to his last silver piece'. His services are hired by a wizard whose castle has been taken over by a warlock. The warlock has also found the wizard's Magic Ring of Power which must be returned. The player must navigate the castle, solve problems and avoid booby traps set by the warlock in order to recover the magic ring for the wizard. The adventurer must also search for treasure and deposit it in a safe which he can then keep as payment.
Source: Wikipedia, "Castle_of_Riddles," available under the CC-BY-SA License.