How do you get to the amulet?

I've got quite a way into the game (DizzyAGE version), but have now run into a brick wall regarding getting the amulet. I know where it is (after looking at the map) but haven't the faintest idea how to get to it. I've tried everything I can think of, with very little success. All I've got left to use is the jewelled dagger, but it doesn't seem to make any difference. Any help would be very welcome.

try the jewled dagger somewhre crystaly

Yes, done it now. I hadn't gone down the trapdoor far enough to find the diamond; that's why I was having no luck with the dagger (cringes with embarrassment).

Thanks for the tip, gazbangor.