Er, um, so okay - it's not really that much of a puzzle game, but I'm desperately running out of the things. So just pretend it's not here or something.
Anyway, The Sentinal, eh? I'm pretty sure (I wouldn't take my word for it, though) that it was the first solid 3D game on the Spec. And what happens is that you're this robot thingy, and there's this sentinal thingy way above you who turns around slowly. If he looks at you then you start dying, so you must climb up to his level by creating rocks and trees and things. and eventually absorb him. This may all sound very complicated, but once you've got into it, it really is lemon peasy and very enjoyable into the bargain, despite the large pauses during play which do tend to hinder things a bit.
Spooky solid 3D vector graphics give this game a very different look to the others we've covered, but it's a puzzler nonetheless. (And quite a good one too.)