Hers's what the walkthrough says...
"Go back into the large chamber and use the crystal
to call the elevator."

Is this the big room just before going down the stairs
to get the crystal. Is it the fancy door with the 2 skulls
on either side. If so then I tried to use the crystal on
this door and nothing happens.

There should be a capsule on the wall where you can place the crystal. In the room you come to when you go down the broken staircase, you will see a painting on the far right. Face that and look to your left, you will find the gem keyhole there.

Welcome to the board, PhilM13!!!

Hope you found the crystal shape hole by now and have ridden the elevator!

Later you will need to ride the top of the elevator too!

Good Luck!

Wyv