As you may have read elsewhere on this website, there is an ATM near the railway crossing in Mezimestí. If you withdraw money then the machine asks if you want to pay in Czech crowns or in Euros. Always choose to pay in Crowns. The cash withdrawal of Kronen will then be deducted from your bank account at a favorable rate.
I pinned 10,000 CZK today. If I had opted to pay in Euros, I would have had a very unfavorable course (see photo: € 439.08). I have chosen to withdraw my account in CZK (circled in red). My account has been written off € 400.35 (Exchange rate 1€ = 24,978144 CZK). So the difference this morning was almost 10%!).