Here are a couple of Rhode Island sand castles from Crescent Beach (one made by inverting buckets, one made with the drip technique I favored as a kid) and an elaborate castle that Suzanne photographed when she was in Copenhagen earlier this month.
This website promises to teach you how to make the perfect sand castle. It involves keeping the sand moist at all times so the castle doesn’t crumble.
Suzanne's Mom's Blog 
I super-like. I was looking for something fun and relaxing and without the press of a crowd to do this weekend. I’m going to the beach to make a sandcastle very soon!
That’s great, Tracy Lee! I will be watching for pictures of your castle on your site, http://tracyleekarner.com/.
No sand castles today–it’s raining! (I thought about putting on my gortex and going to the beach anyway (if you’re supposed to keep the sand wet, it’s probably easier to build in the rain, right?) But it’s too warm, I’d swelter in that suit…
Well, too wet is also not good. Another time.
Oh, yes, the drip technique is the approach favored by true masters of the craft!
Makes me think of the natural “castles” and “spires” formed by dripping — stalactites and stalagmites.