John McBildit's Staircase Problem is one of my favorite math projects for introducing or reviewing the different strategies to solve a math problem. It takes just 2-3 days, and is a great intro to the variety of ways to approach math problems and explain mathematical thinking. It can be an easy project to do before or after Spring Break to review or get back into the swing of things in math.
If you don't want to do this as a whole class math activity, I've recently given the problem to a few of my second grade students who want to be able to do math challenges, but need a less "challenging" challenge option. :)
Hop on over to my blog for day by day lesson instructions as well as the freebie.