These might not look the best, but someone may have some ideas for improvment. I made these with the leftover concrete from my tiki project. One part concrete, one part sand, water, and powder concrete coloring. Then I dug a hole in my kid's sand area for a mold. Then just build the cave with some interesting holes. I put a little sand over these while curing to keep them from drying too fast and cracking. The sand brushes off a little after drying, so it will show if your substrate is a different color.
