From the lightning tower where the 4 keys need to be delivered, there is a little tomb in the back across a small pond that the player needs to access to get one of the keys.

I went there three times and got stuck in the sand twice. I got stuck by swimming over the surface of the water with the teleporting motion of the Vive controller, but when I got to the other side, where the water was shallow, it seemed I was teleported in a way where my head was above water but my legs were buried under the sand. Trying to move from there was impossible. This never happened to me swimming anywhere else so I don't know if it was bad luck or if there's something about the geometry in that area that causes this.

The first time this happened I loaded an earlier save, and the second I used to teleporting device to get free.