We visited several sand formations including the red sand dunes in Fairy Stream and Red Canyon, the white sand dunes in Bau Trang as well as the yellow (gold) sand dunes. If not for the cluster pine trees by the lake, one would think it's a desert in Africa or the Middle East. In Bau Trang, you can ride a horse up the dunes or slide down on a makeshift sled which small kids will tout to you.
We booked this afternoon tour in Ham Tien Beach. It was US$14 per person but we had the 4x4 all to ourselves. The ride around was a blast as I enjoyed the wind hit my face as we stood behind the jeep.