Chickpea and I made this ice heart a few weeks back. We went on a walk and gathered up little bits of nature that we found. We took them back home and talked about them all and then put them in a little cake pan, filled it with water and a looped string and popped it all into the freezer. The next day we hung it outside and watched it melt, revealing more layers and changing shape as we played outside.
I think these could be really fabulous if you lived in a colder climate than us where they stayed frozen for a longer amount of time - you could decorate whole trees with different ornaments. I even thought a garland of them made in a fun shaped cupcake pan like hearts or stars would be cool too.