Math Simulation Activity

While searching for great math ideas to incorporate into my classroom I stumbled upon http://mathbydesign.thinkport.org/  This site allows students to do various math calculations to design a park and there is another option as well.  They can sign in and save their progress.  From the few minutes I played with this site, it would be far to challenging for my 5th grade students (many of them anyway, might high ability students will LOVE this) but I wanted to share the site so those of you who teach higher level math can benefit from the site.  :)  Enjoy!