A 3.5 cm long Nothosaur vertebra from a triassic "Bonebed" in a quarry in southern Germany (Baden-Württemberg).
The prep work was kinda hard, because the stone is extremely hard and the fossil is very fragile. So I think it took about 3 hours.
Here is a picture of the unprepped fossil:
As you can see I decided to restore a bit, but nevertheless I am satisfied with the result