Arthur: The Quest for Excalibur (1989), an illustrated text adventure by Bob Bates.

As described on the box:

In the days before Camelot, when magic and evil rule England, a sword sheathed in stone appears in a quiet churchyard. Engraved upon it are the words which form your destiny. For you are Arthur, the son and true heir of the High King, Uther Pendragon.

But there is more to asserting your claim than wresting free the sword. The sword in the stone disappears -- stolen by the evil King Lot.

To win it back, you must develop the kingly qualities of wisdom, chivalry, and experience, qualities that will also prove you worthy of the throne. And you must do it all within three days, or Lot will usurp your legacy.

You are assisted by Merlin the Enchanter, who grants you the power to transform yourself into a variety of animals. Now you can explore the kingdom as no one has before: from the sky, from rivers and lakes, from on -- and under -- the earth. How you use this power, and how you solve the myriad puzzles that confront you, will determine your success in your quest.