Every year, I start my 4th and 5th grade math classes off with a problem solving unit for the first days of school to encourage thinking deeper and learning accountable talk. (could also be used during testing weeks or before breaks) The last few years, I have been inspired by Jo Boaler's book "Mathematical Mindsets" and her work "Week of Inspirational Math" at youcubed.org. This quest combines selected lessons from the 3-5 collection with a quest. Lessons pdf's are attached so you don't have to search for them. However, you could easily replace with other lessons of your choice with minor tweaks to story line.