It's easy. Never dealt with €20M but the principle is scaleable, you smurf the money in ~€10k amounts through a network of trusted money mules. You buy a cash-only/mostly business like a car wash, take-away etc., rent half-a dozen shops and pump the cash through those, banks won't usually complain about cash coming in like this. €5k * 52 * {y stores}. There are entire areas of shops in some cities where no-one goes in but the business has a healthy turnover.
There are lots of other methods too but those are trade secrets. "I could tell you but" etc. Easy 'big bang' methods like houses Rolls-Royces and art no longer work easily in most jurisdictions (oddly, apparently still in Oz from other comments). I miss the days when you could walk ito a bank with a shopping bag full of bundles of notes, I've done that - fun.