"Quest 20 - Solve the Riddle of the Ruby.
Lord Inspectron at map entry 8 in Castle Blackridge North in overland map area B1, map entry 3, quests you to solve the Riddle of the Ruby. This probably has to do with the Ruby Whistle found in overland map area C1, map entry 3 as part of quest 3. Completion may depend upon finding the Stronghold in the Enchanted Forest in overland map area B3, map entry 4, and blowing the Ruby Whistle twice to enter. Return to Lord Inspecrton to claim the reward of 8000 XP each and quest 21."

Gee, that's not helpful. I went down there (AGAIN), blew the whistle twice, entered, got out, and he still doesn't give the reward.

Nevermind, the walkthrough was incorrect. Found another walkthrough that gave the correct solution.

6. Solve the Riddle of the Ruby: Warrior's Stronghold at B2

x9,y9. Difficult to get to. The riddle is at x7,y11 in the

middle of the room. The answer is crystal, and giving the

correct answer will get you a crystal key.