I'm told that MacKenzie already mentioned our new sandbox, but I thought I'd discuss the construction process a little bit. We decided to make a 6' x 6' box (enough room to hold multiple children) based somewhat on this design, so I bought four 2" x 6" x 12' cedar boards, and cut them all in half, to make a box with 12" tall sides. First I put four half-boards together with 2.5" deck screws to make a square. Then I primed and painted the square (I elevated the square on paint cans and did this now so I wouldn't have to paint it when it is sitting on the ground).
I also attached weed-control fabric to the bottom of the square with staples. My raised garden beds have had some issues with grass growing in them, and I don't want that in the sandbox, so I did this. The tutorial at the link above actually involved making a wooden bottom, but I thought that was excessive, especially since it rains a lot here, and I want the water to be able to drain.
I dug out the grass where the sandbox was to be placed, to further reduce the likelihood of grass issues.
Then I put the square in place, and pounded an 18" wooden stake into the ground, inside the square, at each corner. I left 5.5" of stake protruding above the square, and screwed each stake to the square with 1.5" screws. Then I put built another square atop the existing one, attaching the boards to each other at the corners, and then to the stake. Then I painted everything (all boards got one coat of primer and two of high-gloss paint).
After this was done, I added 24 bags of sand to the box (1200 lbs. worth, to make it 4" deep), with a bit of guidance.
Finally, I added seats in two of the corners, so mom and dad have a place to sit while Lucy plays in the sand.
MacKenzie would like a cover over this, to keep cats out. I want to allow rain to get in the box, to keep the sand moist, so I'll make a cover with hardware cloth and a frame of 1" x 2" x 6' wood strips, or something like that.
If you love this sandbox, feel free to stick it up on Pinterest. No really, I insist.
Update: I made a cover for the sandbox, something that will keep out critters but allow rain and sunshine to enter. I used 1" x 4" cedar boards, poultry wire, and staples. I just lay it on the box, and set it aside when it is playtime.