Germany was made to pay reparations to the allies due to the Treaty of Versailles which meant that they needed to print money and really fast which ended up causing hyper inflation. There are photos on the internet of kids playing with stacks of money because it just wasn't worth anything. How did they end up stabilizing their economy? what happened to all of the money that they had just lying around?
They sorted the problem by introducing a new currency, the rentenmark, which you could exchange your masses of worthless marks for in return for a reasonable amount of the new currency. I assume the old money was probably burnt after collection by the banks and government. I’ve seen photographs of people, during hyperinflation, burning their notes as fuel because the money they were burning was worth less and burnt longer than the fuel they could buy with it