It sounds like you do have the pass. Then, all you have to do is walk Beethro back through the City to the Slaymasters' Hall. It's a long walk to get there properly. When you get there, if you stand in the right place, it will take you inside.
I would post a room image for you, but since you don't have CaravelNet, you wouldn't be able to see it. When you are in front of the Slaymasters' Hall
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×The City 5N3W stand on square (17,28). If you don't have the pass, nothing will happen. If you do have the pass, it will take you inside. (Right click with your mouse to see what square you're on.)