Inexpensive Summer Fun for Kids at Home

I just read the article - Fun, INexpensive Vacations for Your Home - that was featured a few weeks ago and I think these ideas are great.

While my kids are home in the summer, I try to find fun things to do at home. One project that we love is making homemade paper. You can buy materials from a craft store or use things you have around your house. There are lots of instructions online. We even found an old screen in the garage that was useful. We then use the paper to write letters to grandparents.

Anyone have any other ideas for summer projects?