With its volatile currency and dysfunctional banks, the country is the perfect place to experiment with a new digital currency. ... His occupation is one of the world’s oldest, but it remains a conspicuous part of modern life in Argentina: Calle Florida, one of the main streets in downtown Buenos Aires, is crowded day and night with men and women singing out “cambio, cambio, cambio, casa de cambio,” to serve local residents who want to trade volatile pesos for more stable and transportable currencies like the dollar. For Castiglione, however, money-changing means converting pesos and dollars into Bitcoin, a virtual currency, and vice versa. ... That afternoon, a plump 48-year-old musician was one of several customers to drop by the rented room. A German customer had paid the musician in Bitcoin for some freelance compositions, and the musician needed to turn them into dollars. Castiglione joked about the corruption of Argentine politics as he peeled off five $100 bills, which he was trading for a little more than 1.5 Bitcoins, and gave them to his client. The musician did not hand over anything in return; before showing up, he had transferred the Bitcoins — in essence, digital tokens that exist only as entries in a digital ledger — from his Bitcoin address to Castiglione’s. Had the German client instead sent euros to a bank in Argentina, the musician would have been required to fill out a form to receive payment and, as a result of the country’s currency controls, sacrificed roughly 30 percent of his earnings to change his euros into pesos. Bitcoin makes it easier to move money the other way too. The day before, the owner of a small manufacturing company bought $20,000 worth of Bitcoin from Castiglione in order to get his money to the United States, where he needed to pay a vendor, a transaction far easier and less expensive than moving funds through Argentine banks. ... Avalancha offers customers a 10 percent discount when they use the virtual currency, because accepting credit cards generally ends up costing Avalancha more than 10 percent as a result of the vagaries of the Argentine financial system.