Argentina's foreign-exchange market is going underground. As the government restricts access to foreign currencies, Argentines seeking hard-to-get dollars have been pushed into "cuevas," or "caves"--clandestine operations where customers pay dearly to exchange pesos for greenbacks.

A customer who visited one in a Buenos Aires suburb recently described a cramped antique shop where an improbable group of would-be customers milled about, surrounded by stained-glass lamps and plush love seats.